Effects Of Litter Removal Research Articles

Effects of Litter Removal and Biochar Application on Soil Properties in Urban Forests of Southern China

Urban forests are crucial components of cities, serving as vital ‘green lungs’ that embody urban civilization and sustainability. Despite their significance in maintaining the urban environment and ecological functions, management practices for urban forests can be unreasonable at times. This study investigated the impact of two common practices, litter removal and biochar application, on soil properties in an urban forest in Changsha city, China. The aim was to understand how these practices affect soil carbon, nutrients, and microbial activity in urban settings. The results showed that soil water content (SWC), pH, available phosphorus (AP), and soil microbial biomass carbon (SMBC) were significantly reduced in areas where litter was removed compared to areas where litter was retained. Conversely, biochar application led to a significant increase in SWC, pH, AP, and SMBC. The treatment alone had no significant effects on total nitrogen (TN), soil organic carbon (SOC), and soluble soil organic carbon (SSOC) in the examined urban forests. However, the SOC and SSOC contents significantly increased over time with biochar application. Our results demonstrated that the influences of litter removal and biochar application on soil property were attributed to the regulation of AP and SMBC in the studied urban forests. This study provides a scientific basis and reference for understanding the sustainable management of urban environments and guiding future conservation efforts in urban greening spaces.

Effect of Litter Removal and Addition on Root Exudation and Associated Microbial N Transformation in a Pinus massoniana Plantation

In forest ecosystems, variations in aboveground litter input caused by global changes, substantially alter soil N cycling. In field-grown plants, few studies have directly measured root exudation rates and quantified their effects on N transformations under litter manipulation. We quantified soil N transformation rate responses to litter manipulation in a Pinus massoniana plantation, and unravelled the effect of root exudation on soil N transformations. We measured in situ P. massoniana root exudation rates as well as soil microbial biomass, soil C and N concentrations, the activities of four soil enzymes involved in soil N transformations, and net N mineralization and net nitrification rates after experimental litter removal and litter addition treatments. Litter removal and litter addition treatments had little impact on soil C and N concentrations, microbial biomass, soil enzyme (urease, hydroxylamine reductase, nitrate reductase, and nitrite reductase) activity, and net N mineralization rates. However, both litter removal and addition increased net N nitrification rates. Additionally, litter removal significantly decreased root C exudation rates (in April 2021 and annually), whereas litter addition had no significant effects on root C exudation rates across all seasons. Furthermore, root C exudation rates were positively associated with urease and nitrate reductase activities, but negatively associated with hydroxylamine reductase and nitrite reductase activities, as well as net N nitrification rate. Overall, we demonstrated that root exudates may be an important physiological adjustment by which trees respond to changes in litter input caused by global environmental changes, regulating underground N biochemical processes. Furthermore, we provide new evidence from root exudates for understanding the potential influence of litter inputs on soil N cycling. A strong correlation exists between root exudates and N transformation, shedding new light on the dynamics of rhizosphere nutrient cycling crucial for maintaining forest ecosystem stability and productivity under changing environmental conditions.

Nitrogen enrichment amplifies the effects of litter treatments on soil microorganisms and ecosystem functions in grazed and non-grazed grasslands

Litter removal or addition and nitrogen (N) enrichment are two important methods for restoring grasslands. Despite the litter alteration and N enrichment effect on soil microorganisms in different ecological systems of independent have got the good evaluation, it is still unknown how N enrichment modifies the effects of litter removal and addition on soil microorganisms and ecosystem function in different grasslands. Here, we conducted two independent experiments to assess the effects of litter addition/removal and N enrichment on soil microorganisms and ecosystem functions in a typical grassland. In a litter-removal experiment, we evaluated how N addition regulated the effect of litter removal in a long-term non-grazed grassland. In a litter-addition experiment, we evaluated how N addition regulated the effect of litter addition in a long-term over-grazed grassland. We found that the response of plant communities to removal/addition of litter and N enrichment was relatively minor in both non-grazed and grazed grasslands; the high precipitation during the sampling year may mask the effects of the litter and N treatments on plant community. Litter addition in the grazed grassland increased fungal and AMF biomass and decreased bacteria: fungi ratio, but litter removal in the non-grazed grassland had only minor effects on soil microbial variables. Litter removal in the non-grazed grassland and litter addition in the grazed grassland had different effects on soil carbon (Cmin) and N mineralization (Nmin), but N enrichment consistently reduced soil Cmin and Nmin in non-grazed and grazed grasslands. In addition, N enrichment amplified the effects of litter treatments on soil microorganisms and mineralization. These findings indicate that removal of litter from non-grazed grasslands and addition of this litter to grazed grasslands may help to restore grasslands, and the amount of N enrichment should be adjusted to optimize the positive effect of nitrogen enrichment and weaken the negative effect of nitrogen enrichment. Overall, our experimental results revealed that the effects of litter treatment on soil microorganisms and mineralization in grazed and non-grazed semi-arid grasslands are amplified by N enrichment.

Responses of aboveground litterfall respiration to unexpected snowfall events in Ailao subtropical forests in Southwest China

Soil respiration, the second largest CO2 flux in terrestrial ecosystems, involves the microbial respiration of litter from aboveground sources, belowground litter and root respiration, from rhizodeposition. In the subtropical forests of the Ailao Mountain, a chamber with automated CO2 efflux was set up with two treatments: a control treatment with litterfall to measure the total soil respiration (RT) and a litter removal treatment to measure aboveground litterfall respiration (RL). This study aimed to examine the responses of RL to unexpected heavy snowfall events and soil temperature (ST), soil moisture (SM), rainfall (RF), total litterfall (TL), litter water content (LWC), nitrate nitrogen (NO3−-N), and ammonium nitrogen (NH4+-N). The period of the study was divided into two: before the heavy snowfall event (BS) and during and after the heavy snowfall event (AS). The rate of RL was slightly decreased in AS (1.18 ± 0.03 μmol CO2 m−2 s−1) compared with that in BS (1.19 ± 0.02 μmol CO2 m−2 s−1). The relationships between RL and ST, SM, RF, and LWC, respectively, were all statistically significant (p < 0.05) in both periods. However, the relationships between RL and TL and NH4+-N, respectively, were not statistically significant for either period. The relationship between RL and NO3−-N was statistically significant for AS but not for BS. The relationship between RL and RF was statistically significant from 2011 to 2018. The temperature dependence of soil respiration was higher in BS than in AS, and the effect of litter removal was 2.55 % and 2.32 % for AS and BS respectively. The results indicate that current global terrestrial models underestimate RL trends for the feedback of global climate change in subtropical forests.

Restoration of subtropical grasslands degraded by non‐native pine plantations: effects of litter removal and hay transfer

Pinus plantations create strong ecological legacies that persist after their removal. We evaluated the effectiveness of pine litter removal (manually or through controlled burns) and hay application for the restoration of South Brazilian coastal grasslands degraded by pine plantations. We installed the experiment 1 year after cutting trees and sampled the vegetation 3 months, 1 year, and 2 years after initiating the experiment. We used generalized linear mixed model to assess treatment effects on plant cover, richness, and pine reestablishment. We used nonmetric multidimensional scaling and indicator species analysis to evaluate changes in species composition over time and in the association of individual species with treatments and reference area. Species richness and vegetation cover did not differ between manual and burn treatments but were higher than in the control. Hay application enhanced vegetation cover by the end of the experiment in all treatments. Hay application enhanced richness initially, but after 2 years the effect persisted only in the burn treatment. Burned plots showed less pine establishment than plots with manual litter removal. Hay‐addition plots contained indicator species present in the reference area. Our results suggest that passive restoration (i.e. only cutting of pine) is not sufficient to restore grasslands altered by afforestation, as residual pine litter constrains the reestablishment of native vegetation. In addition to the benefits of litter removal, our results indicate that hay transfer can overcome seed limitation of grassland species and burning can reduce recolonization by pine.

Response of Soil Net Nitrogen Mineralization to a Litter in Three Subalpine Forests

Forest litter accumulation can regulate the soil microclimate and alter nutrient distribution, but the effects of litter quality and seasonal differences on soil nitrogen (N) mineralization are still uncertain. The effects of litter change on the rates of net N mineralization, nitrification, and ammonification were studied through in situ incubation experiments in coniferous, mixed, and broad-leaved forests in the eastern Qinghai–Tibetan Plateau. Two litter treatments were established, one to allow the litter to enter the soil normally (remain litter) and the other to prevent the litter from entering the soil (remove litter). Soil samples were collected at the freezing (FS), thawing (TS), early growing (EGS), late growing (LGS), and early freezing (EFS) seasons during the 1.5-year incubation period. Compared to coniferous forests, the effects of litter removal on the net ammonification, nitrification, and N mineralization rates were more pronounced in broad-leaved forests, mainly during the growing and thawing seasons. Structural equation modeling indicated that microbial biomass N (MBN) was a common factor affecting the net ammonification, nitrification, and N mineralization rates in the three forest soils. The coniferous forest microbial biomass carbon (MBC), mixed forest soil moisture, broad-leaved forest soil N concentration, and C:N ratio were the unique influencing factors of the different forest types. The results showed that the effect of litter distribution on the soil net N mineralization mainly depended on forest type and season, suggesting that the litter composition and productivity in different seasons and forest types may alter the soil N cycling processes in subalpine forest ecosystems.

秦岭天然林凋落物去除对土壤团聚体稳定性及细根分布的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 秦岭天然林凋落物去除对土壤团聚体稳定性及细根分布的影响 DOI: 10.5846/stxb201912272807 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 农业部农业环境重点实验室开放基金(K4030217149);国家林业公益性行业科研专项(201304307) Effects of litter removal on soil aggregate stability and distribution of fine roots in natural forests of Qinling Mountains Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:研究凋落物去除对秦岭天然林土壤团聚体稳定性及细根分布特征的影响机制,为森林生态治理提供理论依据。结果表明:(1)凋落物去除导致云杉林10-40 cm土层土壤中粒径大于0.25 mm水稳性团聚体含量(WR0.25)较对照显著降低(P<0.05);混交林10-40 cm土层的大于0.25 mm机械稳定性团聚体含量(DR0.25)显著降低(P<0.05);红桦林表层0-10 cm土壤团聚体的平均质量直径(MWD)显著降低(P<0.05);(2)凋落物去除导致三种天然林0-20 cm土层的细根生物量密度(FRBD)较对照显著降低44.18%-57.24%,细根体积(FRV)显著降低24.64%-60.41%;三种天然林中红桦林0-40 cm各土层的FRV最高;(3)凋落物去除导致云杉林0-40 cm土层的土壤容重较对照显著增加5.24%-13.04%,三种天然林0-40 cm土层的土壤有机碳含量显著降低7.92%-25.21%,全氮含量显著降低10.17%-18.10%;(4)相关分析表明,云杉林土壤的团聚体破坏率(PAD)和土壤不稳定团粒指数(ELT)与FRBD、细根根长密度(FRLD)和FRV均呈极显著负相关,混交林土壤的PAD与FRBD呈极显著负相关关系(r=-0.814),红桦林土壤团聚体MWD与FRBD、FRLD和细根比根长(FSRL)均呈显著负相关关系(r=-0.777、-0.771和-0.786)。综上,凋落物去除在总体上降低了天然林土壤团聚体的稳定性及有机碳和全氮含量,并且不利于林木细根的生长。 Abstract:The objective of this study is to investigate the effects of litter removal on the characteristics of soil aggregates stability and fine root distribution so as to provide theoretical bases for vegetation restoration and ecological protection in Qinling Mountains. Results indicated that (1) the litter removal significantly decreased the percentages of >0.25 mm water-stable aggregates (WR0.25) in 10-40 cm soil layer (P<0.05). The percentage of >0.25 mm mechanical-stable aggregates (DR0.25) in 10-40 cm soil layer of mixed forest was also decreased significantly (P<0.05). The mean weight diameter (MWD) of aggregates in 0-10 cm soil layer of Betula albosinensis forest was decreased (P<0.05) by litter removal. (2) By litter removal, the fine root biomass density (FRBD) in 0-20 cm soil layer of the three forests significantly decreased by 44.18%-57.24%; the fine root volume (FRV) significantly decreased by 24.64% to 60.41%. The FRV in 0-40 cm soil layer of Betula albosinensis forest was the highest among the three forests. (3) After 3-year litter removal, the soil bulk density in 0-40 cm soil layer of Picea asperata forest significantly decreased by 5.24%-13.04%. The soil organic carbon contents in 0-40 cm soil layer of the three forests significantly decreased by 7.92%-25.21%, and the contents of total nitrogen significantly decreased by 10.17%-18.10%. (4) The results of correlation analysis showed that percentage of aggregate destruction (PAD) and unstable soil aggregate index (ELT) of Picea asperata forest soil had significantly negative correlations (P<0.01) with FRBD, fine root length density (FRLD), and FRV. The PAD of mixed forest soil showed a significantly negative correlation (P < 0.01) with FRBD (r=-0.814). The aggregate MWD of Betula albosinensis forest soil had significantly negative correlations (P < 0.01) with FRBD, FRLD and fine specific root length (FSRL) (r=-0.777, -0.771 and -0.786). Overall, the litter removal decreased the stability of soil aggregates, the contents of soil organic carbon and total nitrogen in soils of natural forests, which also inhibited the growth of fine roots. 参考文献 相似文献 引证文献

Litter removal effects on dynamics of soil humic substances in subalpine forests of western Sichuan, China

Litter removal effects on dynamics of soil humic substances in subalpine forests of western Sichuan, China

Litter removal exerts greater effects on soil microbial community than understory removal in a subtropical-warm temperate climate transitional forest

Litter and understory play important roles in maintaining structure and functions of belowground ecosystems in forests. However, how litter and understory affect soil microbial community is unclear. As part of a three-year (2016–2018) manipulative experiment, this study was designed to evaluate the effects of litter and/or understory removal on soil microbial community in a coniferous-broadleaved mixed forest of the subtropical-warm temperate transition zone in Central China. The results showed that soil moisture, NO3−-N, NH4+-N, and dissolved organic carbon were decreased under litter removal, but remained unchanged under understory removal. Total, bacteria, and actinomycetes PLFAs were significantly reduced by 11.2%, 16.3%, and 11.0% under litter removal, and by 10.1%, 13.3%, and 12.5% under understory removal, respectively. Both litter and understory removal suppressed network complexity of soil microbial community, but litter removal showed much stronger impacts on the biomass (−14.9 mg kg−1 vs. −10.9 mg kg−1) and composition (−7.77% vs. −2.89%) of bacteria (including gram-positive and gram-negative bacteria) as well as fungi to bacteria ratio than understory removal. Changes of soil NH4+-N and moisture might be primarily responsible for the inhibitory effects of litter removal on soil gram-positive and gram-negative bacterial biomass, respectively. Our findings highlight the contrasting responses of soil microbial community to litter and understory removal and would facilitate the mechanistic understanding of these two management practices on belowground ecology in climate transitional forests.

Long‐term litter removal rather than litter addition enhances ecosystem carbon sequestration in a temperate steppe

Abstract Global change can greatly affect plant productivity and subsequently litter input to soil, with potential impacts on soil carbon (C) fluxes. However, the effects of litter layer in mediating C cycling and budget at an ecosystem scale are still not clear. As part of a long‐term litter fall manipulation experiment in a temperate steppe on the Mongolian Plateau, this study was conducted to explore effects of litter removal and addition on ecosystem C budget and the associated mechanisms. Overall, litter removal enhanced photosynthetic active radiation (PAR) at soil surface by 31.0%, but litter addition reduced it by 26.5%. Litter removal decreased soil inorganic nitrogen (SIN) content at the depth of 0–10 cm by 13.6%, but litter addition enhanced it by 14.1%. Litter removal increased legume abundance by 131.1%, whereas litter addition enhanced grass abundance by 30.7% but decreased forb abundance by 33.1%. Litter removal increased gross ecosystem productivity (GEP) through enhancing PAR and legume abundance, whereas litter addition elevated GEP by changing plant community composition mediated by decreasing PAR and increasing SIN. Litter removal did not affect ecosystem respiration (ER), but litter addition stimulated ER by 14.9%. Therefore, while litter addition did not affect net ecosystem productivity (NEP), litter removal surprisingly enhanced NEP by 23.9% over the later 7 years. Our findings highlight that more above‐ground litter input derived from biomass production may not necessarily result in a larger ecosystem C sink in grasslands under global change scenarios in the future. On the contrary, proper litter removal may be an effective way to increase the ecosystem C sink in grassland management. A free Plain Language Summary can be found within the Supporting Information of this article.

Response of methane emissions to litter input manipulation in a temperate freshwater marsh, Northeast China

The photograph of the field experiment of different litter input manipulations in situ and the treatment effects on CH 4 fluxes during observations in 2015 and 2016. Abbreviations: NL, no aboveground litter; DL, double litter; CK, control; AR, standing litter removal. • We conducted a two seasons litter input manipulation experiment in a freshwater marsh. • Litter input manipulations obviously affected CH 4 emission and surface DOC contents. • Litter removal induced higher soil temperature, DOC content and CH 4 emission. • The abundance of methanogens in surface soil relied on the ways of litter manipulation. Plant litter plays an important role in regulating CH 4 emission in wetland ecosystems. Our knowledge of the impacts of plant litter on CH 4 budget is important for understanding the response and feedbacks of wetland ecosystems to climate warming. Nevertheless, the effects of plant litter on CH 4 emission and temperature sensitivity (Q 10 ) are not clear under the background of global change. In this study, a field litter inputs manipulation experiment with four treatments including no aboveground litter (NL), standing litter removal (AR), doubled litter input (DL) and controls (CK) was conducted to study the effects of litter manipulations on CH 4 emission in a seasonal inundated freshwater marsh over two growing seasons of 2015 and 2016 in the Sanjiang Plain, Northeast China. Results showed that CH 4 emission was significantly associated with altered litter input over the observation period. Compared with CK, the cumulative CH 4 emission increased by 105.83%, 42.20% and 42.50% for NL, AR and DL treatments, respectively, in 2015, and the values were 199.04%, 115.55% and 17.55%, in 2016. Variances of CH 4 emission were more sensitive to litter removal effects. Altered litter input also significantly affected the dissolved organic carbon (DOC) concentration ([DOC]) in surface pore water. DL and CK treatments with lower soil temperature had lower [DOC] than litter removal treatments of NL and AR. The abundance of methanogens among the four treatments exhibited synchronous change with DOC over the observation period. The Q 10 values of CH 4 emission didn’t show consistent changing patterns with those of DOC among different litter input treatments, which was probably due to the different temperature sensitivity of dominant methanogen types. Due to its great effects on soil microclimate, substrate availability and the concomitant variation in temperature sensitivity, our results highlighted that plant litter effects should be incorporated into the current process-based CH 4 biogeochemical models to predict future CH 4 fluxes from natural wetlands under the background of global change.

Effects of litter removal and nitrogen addition on carbon and nitrogen in different soil fractions in a subtropical broad-leaved forest.

The increasing nitrogen deposition due to human activities has impacted forest ecosystems to a large extent. The organic carbon and nitrogen released from decomposing litters play an important role in the formation, stability and transformation of soil organic carbon and nitrogen. We collected soil samples from a subtropical evergreen broadleaved forest experiment with nitrogen deposition [control (0), LN (75 kg·hm-2·a-1), HN (150 kg·hm-2·a-1)] and litter control (litter retained and litter removal) for eight years. After extracted by solution of K2SO4, Na2B4O7, Na4P2O7, NaOH, H2SO4, Na2S2O4 and HF step by step, carbon and nitrogen in each extraction was analyzed. The results showed that overall most of soil carbon and nitrogen existed in the Humin fraction, accounting for 33.5% of the total carbon and 33.3% of the total nitrogen. The soluble total carbon and nitrogen extracted by Na2B4O7 solution was the highest, followed by NaOH and Na4P2O7 solution. The soluble total carbon, soluble total nitrogen and soluble organic nitrogen of soil extracted by three reagents accounted for 46.2%, 47.9%, and 76.5% of the total extractions, respectively. In addition, nitrogen addition significantly increased carbon and nitrogen content in Na2S2O4 and Humin fractions. Litter removal reduced carbon content in Na2B4O7, H2SO4, Na2S2O4 and Humin fractions, and nitrogen content in NaOH, HF and Humin fractions. The nitrogen content in the K2SO4 extraction was significantly increased by both litter remained and nitrogen addition. Our results demonstrated that litter and nitrogen added could mutually affect carbon and nitrogen concentration of soil fractions with different chemical stability, with consequences on the process of soil carbon and nitrogen.

Hydrologic alterations impact plant litter decay rate and ecosystem resilience in Mojave wetlands

Understanding ecosystem processes is vital for effective restoration of degraded ecosystems, especially wetlands. Restoration has become a necessity for management and conservation of the federally endangered Amargosa vole (Microtus californicus scirpensis) endemic to small, bulrush (Schoenoplectus americanus) dominated wetlands in the Mojave Desert. Recent data indicate catastrophic decrease of the vole population and its habitat from local alterations to hydrology, combined with diminished decomposition rates of bulrush, persistence of plant litter, and minimal plant growth except along narrow margins along stream edges. We conducted a series of three field and one greenhouse experiment(s) testing the effect of (1) moisture level on plant decay rate, (2) litter removal on plant regeneration, (3) the interactive effect of litter removal and moisture level increase on plant regeneration, and (4) potential germination rate of bulrush seeds under multiple hydrologic regimes to understand how hydrologic alteration and litter decay ultimately influences marsh regeneration. Results revealed decrease in water level caused a 20‐fold reduction in decomposition rates of a degraded marsh. Litter removal alone and in combination with water table restoration significantly and positively affected bulrush resprouting (p &lt; 0.0001 for both). Seed bank experiments showed high rates of germination in saturated and flooded soil conditions, emphasizing the potential role of seedlings in ecosystem recovery. This study shows how the interaction of hydrologic change and decreased decomposition can shift an ecosystem toward limits of resilience. These results inform restoration strategies in arid‐region wetlands dominated by plants with slow litter decay where strategic litter removal may beneficially increase plant growth.

Litter removal reduced soil nitrogen mineralization in repeated freeze-thaw cycles

Repeated freeze-thaw cycles (FTCs) can alter the relationships between plant litter and soil nitrogen (N) mineralization in subalpine ecosystems, but little information is available about the underlying mechanisms. Therefore, a controlled soil incubation experiment was carried out to study the effects of litter removal on soil N mineralization during FTCs, and the results indicated that FTCs promoted soil N mineralization more than the continuously frozen or nonfrozen condition did. Litter removal promoted soil ammonium N (NH4+-N) and dissolved organic N (DON) as well as the cumulative N mineralization (CNM) and ammonification, but it reduced the soil microbial biomass N (MBN) in the early stage of FTCs. With an increasing number of FTCs, litter removal significantly reduced the CNM but increased the soil MBN. The modified first-order kinetics model was verified under incubation conditions and predicted a lower soil N mineralization rate in FTCs with litter removal. In addition, the dominant factor impacting soil N mineralization was soil NO3−-N, and soil MBN had a greater influence on soil N mineralization when litter remained than when it was removed. These results further clarify the mechanism driving the effect of plant residues on soil N cycling.

Litter manipulation strongly affects CO2 emissions and temperature sensitivity in a temperate freshwater marsh of northeastern China

Plant litter (including standing litter) modification plays a vital role in wetland carbon (C) balance, which can be greatly altered by global change. Our knowledge of the fundamental function of plant litter in ecosystem respiration (Re) is crucial for evaluating C exchange between the atmosphere and biosphere. However, it is not well understood how litter manipulation could influence the dynamics of Re and its temperature sensitivity (Q10) in wetland ecosystems. In the present study, we conducted a field manipulation experiment with the following treatments of total aboveground plant litter removal (ALR), standing litter exclusion (AR), doubled plant litter (DL) and unchanged litter input (CK) to study the effects of wetland plant litter on Re and Q10 values over two growing seasons (2015 and 2016) in a Deyeuxia angustifolia-dominated freshwater marsh in the Sanjiang Plain, Northeast China. Results showed that wetland Re was significantly affected by different plant litter input manipulations. During the two growing seasons, the Re ranged from 27.16 to 643.61 (ALR), 39.61–690.25 (AR), 136.27–1270.38 (DL) and 72.11–862.42 mg CO2-C m−2h−1 (CK), which decreased by 28.36–68.04% and 15.11–63.23% of the ALR and AR treatments and increased by 15.41–20.59% of the DL treatment compared with CK, respectively. The changes in Re was more susceptible to litter removal effects. In 2016, the mean Re values of ALR and AR treatments decreased significantly compared with the corresponding values in 2015, while it was significantly increased in the DL treatment. The concentrations of NH4+ and DOC, as microbes directly used carbon and nitrogen sources in soil pore water were significantly affected by litter input manipulations suggesting that there are various carbon and nitrogen sources within and outside the plant litter. The Q10 values of Re under each litter input manipulation treatment differed markedly, and the highest value (3.32–4.06) occurred in the total plant-derived litter input removal treatments indicating that the wetland soil was vulnerable to disturbance that prone to carbon losses in the context of global warming. Our results also demonstrated that the Q10 values of the deeper soil (below 15 cm) with vegetation present were lower than that for the other litter removal treatments implying the important function of the carbon sink in this wetland ecosystem. Overall, we recommend that the role of wetland plant litter input to the soil system should be seriously considered when predicting biosphere-atmosphere C exchange model under the background of global climate change.

Effect of nitrogen addition and litter removal on understory vegetation, soil mesofauna, and litter decomposition in loblolly pine plantations in subtropical Argentina

Loblolly pine monocultures have been increasingly expanding in the Atlantic Forest of South America especially in northern Argentina. Pine plantations can modify understory vegetation and soil characteristics due to the management practices and to the dense mulch of pine needles that develop in the forest floor that could affect soil biota and ecosystem processes. Nitrogen (N) addition as expected as atmospheric deposition can also contribute to these changes. The aim of this study was to assess the effect of litter removal and low levels of N addition on understory regeneration, soil mesofauna abundance, and leaf litter decomposition. For this purpose, a completely randomized block design was used. Nitrogen addition had significant effects on understory regeneration promoting creeping herbs, graminoids and shrubs life forms affecting tree establishment and growth. Litter removal treatment showed the same pattern but only promoting the creeping herbs that could also have affected tree species. Decomposition decreased due to litter removal and was slightly increased by N addition. The addition of N decreased the abundance of mesofauna in the mulch, especially Symphypleone (a suborder of Collembola), but the abundance of the soil communities was not affected. Litter removal had a strong impact on these communities because most individuals and species of the mesofauna are present in the litter and not in the soil. This is one of the first studies analyzing the effect of low amounts of N addition and litter removal in subtropical pine plantations and contribute to understand potential impacts of increasing N deposition on biodiversity and soil processes, and to select organisms that may help as bioindicators in assessing impacts on ecological functions in productive ecosystems.

Global effects of plant litter alterations on soil CO2 to the atmosphere.

Soil respiration (Rs) is the largest terrestrial carbon (C) efflux to the atmosphere and is predicted to increase drastically through global warming. However, the responses of Rs to global warming are complicated by the fact that terrestrial plant growth and the subsequent input of plant litter to soil are also altered by ongoing climate change and human activities. Despite a number of experiments established in various ecosystems around the world, it remains a challenge to predict the magnitude and direction of changes in Rs and its temperature sensitivity (Q10 ) due to litter alteration. We present a meta-analysis of 100 published studies to examine the responses of Rs and Q10 to manipulated aboveground and belowground litter alterations. We found that 100% aboveground litter addition (double litter) increased Rs by 26.1% (95% confident intervals, 18.4%-33.7%), whereas 100% aboveground litter removal, root removal and litter+root removal reduced Rs by 22.8% (18.5%-27.1%), 34.1% (27.2%-40.9%) and 43.4% (36.6%-50.2%) respectively. Moreover, the effects of aboveground double litter and litter removal on Rs increased with experimental duration, but not those of root removal. Aboveground litter removal marginally increased Q10 by 6.2% (0.2%-12.3%) because of the higher temperature sensitivity of stable C substrate than fresh litter. Estimated from the studies that simultaneously tested the responses of Rs to aboveground litter addition and removal and assuming negligible changes in root-derived Rs, "priming effect" on average accounted for 7.3% (0.6%-14.0%) of Rs and increased over time. Across the global variation in terrestrial ecosystems, the effects of aboveground litter removal, root removal, litter+root removal on Rs as well as the positive effect of litter removal on Q10 increased with water availability. Our meta-analysis indicates that priming effects should be considered in predicting Rs to climate change-induced increases in litterfall. Our analysis also highlights the need to incorporate spatial climate gradient in projecting long-term Rs responses to litter alterations.

Asymmetric effects of litter removal and litter addition on the structure and function of soil microbial communities in a managed pine forest

Variation in tree litter inputs and understory vegetation caused by human disturbances and climate change in forest plantations can extend to alter forest stability and productivity over time. Here, we explore how tree litter inputs interact with understory plant management to influence belowground processes in a managed forest plantation. We conducted a two-factor nested experimental manipulation of pine litter and understory vegetation in a nutrient-poor Pinus sylvestris var. mongolica plantation. Three levels of tree litter manipulation (ambient litter, litter removal and litter addition) were nested in two levels of understory manipulation (understory intact and understory removal). After two years of manipulation, mineral soils were analyzed for total and extractable C, N and P concentrations, N mineralization, enzyme activities, as well as the microbial community structure (as indicated by phospholipid fatty acids). Litter removal had little impact on C and nutrient cycling as well as microbial biomass and community structure in this low nutrient pine plantation; however, litter addition and the removal of the understory vegetation had large impacts on these processes. Litter addition elevated soil microbial biomass, acid phosphatase and β-1, 4-glucosidase activities, by a much greater degree when the understory vegetation was intact than when the understory was removed. Litter addition also reduced soil available P by 39% when the understory vegetation was intact, and reduced soil available P by 74% and NO3 −–N by 45% when the understory was removed. Litter addition significantly reduced the ratio of Gram-positive to Gram-negative bacteria as well as the ratio between PLFA markers cy17:0 and 16:1ω7. Understory removal reduced the ratio of PLFA markers cy17:0 to 16:1ω7. Our study results show that, in this managed pine plantation, soil microbial community structure and function were more sensitive to an increase rather than to a decrease in pine litter inputs. Further, we found that the presence of understory vegetation can increase soil microbial biomass and alleviate the reduction in available N and P concentrations induced by pine litter addition. Thus, preservation of the understory vegetation is an effective way to maintain the functional stability of managed forests on nutrient-poor soils.

Thinning of loblolly pine plantations in subtropical Argentina: Impact on microclimate and understory vegetation

During the last three decades, the area dedicated to tree plantations in northeast of Argentina has increased five-fold at the expense of the native semideciduous Atlantic Forest. Silvicultural practices such as thinning affect the understory and forest floor incrementing vegetation cover and diversity that may impact ecological functions such as carbon and nutrient cycling and provide food and shelter for wildlife. The aim of this study was to assess the effects of two thinning intensities (50% and 30% of individual removal), and litter removal in the 50% thinning treatment on the understory vegetation of loblolly pine (Pinus taeda L.). The high thinning intensity and the control without thinning were intended to recreate existing management practices in the region. The study was carried out in three Pinus taeda plantations (replicates). Environmental conditions and cover of native understory vegetation were measured during two years after thinning. Canopy openness, solar radiation, air temperature and soil bulk density were higher in thinning treatments than in control plots while soil water content was lower. Vegetation cover and richness increased with intensity of the thinning treatments. Tree saplings differed in the responses according to light requirements and height. Light-demanding species and individuals taller than 0.5m were responsive to thinning increasing coverage, abundance and height, while smaller saplings were more abundant in control plots. No effects of litter removal were observed in understory species richness and plant cover. This study provides evidence that thinning on pine plantations in Northeastern Argentina can contribute in maintaining biodiversity and related ecosystem functions of subtropical forests. Management practices involving lower plantation densities and fewer interventions should be developed to achieve more positive effects.

δ 15N of soil nitrogen pools and their dynamics under decomposing leaf litters in a suburban native forest subject to repeated prescribed burning in southeast Queensland, Australia

Global environmental changes could affect forest productivity and thus organic matter input to soil via litterfall. We conducted a 9-month litter decomposition experiment to examine the effect of litter removal and addition on soil nitrogen (N) dynamics in a subtropical eucalypt forest subject to prescribed burning. Two litter treatments were applied: addition of double litter rates and without any litter addition. In situ 15N pool dilution method was used to determine soil gross N transformation rates, and δ 15N of soil inorganic N pools and their dynamics were also measured. The results showed that the addition of decomposing litters had no significant effect on soil net and gross N mineralization and nitrification rates. Soil N rates showed a pronounced seasonal pattern with higher rates in summer and lower rates in winter, which could be explained by the seasonal variation of environmental conditions such as temperature but not soil water content in this study. The soils had significantly higher δ 15N in NO3 −-N than in NH4 +-N after removing the forest floor, which might result from gaseous N losses via nitrification, denitrification and NO3 −-N leaching during the experimental period. Soil N transformations were not significantly affected by decomposing litters during the 9-month of decomposition. Our findings demonstrate that long-term studies of litter decomposition combined with repeated measurement of soil N transformation rates are needed to fully understand the seasonal patterns of soil N cycling and its response to decomposing litters in forest ecosystems.