Root Trenching Research Articles

Impact of Root Cutting on Acer platanoides and Tilia cordata Tree Stability in Urban Parks: A Case Study in Quebec City, Canada

Trees growing in urban environments are often impacted by maintenance or construction work involving the cutting of roots. Tree protection zones have been proposed to avoid critical damage to the tree. However, despite incorporating quantitative information, they heavily rely on expert judgement that remains to be validated. In a study conducted across six parks in Quebec City, Canada, two commonly found tree species, Acer platanoides L. and Tilia cordata Mill., presumed to be different in terms of vulnerability to root damage, were subjected to a range of trenching treatments. The trees were between 23 and 40 cm diameter at breast height (DBH). A safety factor was calculated relating the turning moment the tree can withstand to the turning moment imposed by high winds likely to occur. The safety factor against uprooting was assessed for each tree before and after root trenching using a non-destructive pulling approach. The effects of tree species, distance to the trench, and their combined interaction were tested on tree stability. The relationship between tree stability and soil texture, tree characteristics, and the number of damaged roots were also tested. Safety factors were initially variable, ranging from 0.5 to 4.5. T. cordata safety factors were lower than those of A. platanoides and influenced by soil texture. Trenching treatments had no effect on the safety factor, even when two perpendicular trenches were dug at 1 m from the stem. No index of the amount of root damaged was significantly related to the safety factor. Root trenching treatments that encroached closer to the tree trunk than the recommended tree protection zones did not affect the stability of both species. Nevertheless, it is essential to recognize that other ecophysiological processes might still be influenced, and long-term monitoring is crucial. Both should be taken into account when determining these zones.

Plant roots are more strongly linked to microorganisms in leaf litter rather than in soil across tropical land-use systems

Tropical soil microorganisms are major recyclers of the biosphere organic carbon. However, the link of tropical microorganisms to the two main pathways of how carbon enters the belowground system, i.e., plant roots and leaf litter, is poorly understood. To investigate the relative importance of these pathways, we studied the response of microorganisms in leaf litter and underlying topsoil to root trenching (exclusion of living roots) and litter removal in tropical rainforests, and how this is altered by rainforest conversion to rubber and oil palm plantations. Unexpectedly, the linkage between living roots and microbial biomass was stronger in litter than in soil across land-use types, indicating that tropical trees prioritize mining for nutrients in leaf litter rather than in soil. After trenching, microbial biomass and basal respiration in leaf litter decreased by 32% and 38%, respectively, whereas microbial biomass and basal respiration remained unchanged in soil. However, fatty acid profiles indicated that root trenching decreased the proportion of total and mycorrhizal fungi in soil, with the effect on mycorrhizal fungi being especially strong when litter was present. Litter removal neither significantly affected microbial biomass nor community structure in soil, suggesting compartmentalization of carbon processing between litter and soil. Overall, the results suggest that across tropical land-use types root-derived resources shape microorganisms in soil and litter via different pathways, with litter microbial communities relying heavily on root-derived carbon, whereas microbial communities in soil being structured predominantly by long-term factors related to land-use history.

Plant carbon removal affects monthly temperature sensitivity of soil respiration during growing season in three typical plantations in the Loess Hilly Region, China

The temperature sensitivity of soil respiration (Q10) is primarily related to annual climate parameters and soil properties in regional models. Changes in climate and soil properties influence plant carbon (C) inputs, which in turn alter Q10 during the growing season. However, the magnitude of this influence remains uncertain. Herein, using meteorological data from small stations and field experiments across three plantations (Robinia pseudoacacia, Caragana korshinskii, and Bothriochloa ischaemum), we investigated the variations in Q10 with respect to the following four treatments: litter removal, root trenching, root trenching and litter removal, and a control group, for 6 months. We found that R. pseudoacacia had the highest relative contribution to atmospheric C release, followed by C. korshinskii, and then B. ischaemum. The Q10 components were month-dependent under C remove in three typical plantations. Litter removal significantly reduced Q10, but the effect of root trenching differed according to the plantation. The variations of Q10 with C removal were primarily controlled by interacting air temperature, air pressure, potential hydrogen, root C, root biomass, soil organic C, and relative humidity, explaining the variations of 81.29–99.33 % (R. pseudoacacia plantation), 89.1–99.76 % (C. korshinskii plantation), and 99.34–99.74 % (B. ischaemum) of the variation in Q10; among them, the cumulative contribution of climate (soil temperature, air pressure, and relative humidity), plants (root C and root biomass), and soil properties (potential hydrogen and soil organic C) accounted for 34.84 %–61.93 %, 12.15 %–32.75 %, and 8.07 %–32.11 %, respectively. These findings demonstrate that C removal variations influenced the Q10, whereas Q10 was also month-dependent. Overall, we recommend that the role of Q10 in the growing season should carefully consider C removal into the soil to improve the biosphere–atmosphere C exchange model in the context of climate change.

Root trenching and stable isotope analysis uncover trophic links of euedaphic collembola species to mycorrhizal mycelium in pine forests

Ectomycorrhizal fungi are a prominent component of the soil biota of boreal forests, but the role of mycorrhizal mycelium as a food source for soil Collembola remains controversial. We addressed this question in a trenching experiment in young (70 years old) and old (180 years old) stands of Scotch pine, combined with stable isotope analysis. Trenching halved the biomass of ectomycorrhizal mycelium, estimated using in-growth mesh bags. In the young forest, the abundance of two euedaphic Collembola species, Mesaphorura yosiii and Willemia anophthalma, decreased after trenching by 99 and 97% respectively, while in the old forest the abundance of Collembola was not affected. In both forests, trenching reduced δ15N values of the dominant euedaphic species Isotomiella minor and W. anophthalma, indicating a shift in trophic niches. Thus, we obtained convincing evidence of species-specific trophic links of euedaphic Collembola species to the mycelium of mycorrhizal fungi.

Combined drought and bark beetle attacks deplete non-structural carbohydrates and promote death of mature pine trees.

How carbohydrate reserves in conifers respond to drought and bark beetle attacks are poorly understood. We investigated changes in carbohydrate reserves and carbon-dependent diterpene defences in ponderosa pine trees that were experimentally subjected to two levels of drought stress (via root trenching) and two types of biotic challenge treatments (pheromone-induced bark beetle attacks or inoculations with crushed beetles that include beetle-associated fungi) for two consecutive years. Our results showed that trenching did not influence carbohydrates, whereas both biotic challenges reduced amounts of starch and sugars of trees. However, only the combined trenched-bark beetle attacked trees depleted carbohydrates and died during the first year of attacks. While live trees contained higher carbohydrates than dying trees, amounts of constitutive and induced diterpenes produced did not vary between live and beetle-attacked dying trees, respectively. Based on these results we propose that reallocation of carbohydrates to diterpenes during the early stages of beetle attacks is limited in drought-stricken trees, and that the combination of biotic and abiotic stress leads to tree death. The process of tree death is subsequently aggravated by beetle girdling of phloem, occlusion of vascular tissue by bark beetle-vectored fungi, and potential exploitation of host carbohydrates by bark beetle symbionts as nutrients.

Effects of Above- and Below-Ground Interactions of Plants on Growth of Tree Seedlings in Low-Elevation Tropical Rainforests on Hainan Island, China

Understanding the effects of above- and below-ground interactions on seedling growth is pivotal for identifying the key drivers of secondary forest succession. However, it is still unclear whether the effects of above- and below-ground interactions of plants are consistent for seedling growth of deciduous and evergreen species. There are two types of broadleaved forests (i.e., tropical lowland rainforest and tropical deciduous monsoon rainforest) in the low-elevation (<800 m) areas of Hainan Island in China. Here, 32 seedling transplanting plots (1 × 1 m2) were established in the tropical lowland rainforest and the tropical deciduous monsoon rainforest, respectively. Four treatments (each with 16 replicates) were carried out to reduce above- and below-ground interactions of plants in the low-elevation forests: removal of vegetation (R), root trenching (T), removal of vegetation and root trenching (R + T), and no vegetation removal or trenching (as the control) (C). Seedlings of four deciduous species and four evergreen species were planted to observe their performance in the experiments. The relative growth rates (RGR) of the seedlings were measured to distinguish the relative effects of above- and below-ground interactions. The photosynthetically active radiation (PAR) was measured as a proxy for above-ground interaction and the root biomass was used as a proxy for below-ground interaction. The relationships between seedling RGR and PAR/root biomass were examined. Results showed that: (1) R and R+T treatments significantly increased the seedlings RGR, but T treatment had no effect on the RGR; (2) the growth rates of deciduous species were greater than those of the evergreen species; and (3) seedling growth rates were increased with more PAR. Our study suggests that above-ground vegetation removal had a stronger effect than trenching on the growth and assembly of tree seedlings in the low-elevation tropical rainforests.

The Impact of Root-Derived Resources on Forest Soil Invertebrates Depends on Body Size and Trophic Position

Forest soil food webs have been assumed to be fueled substantially by root-derived resources. However, until today the flux of root-derived resources into soil animals has been investigated virtually exclusively using isotope labeling experiments, whereas studies on the consequences of disrupting the flux of root-derived resources into the soil animal food web are scarce. We here investigated the importance of root-derived resources for a wide range of soil animals by interrupting the resource flux into the soil of different forest types in Central Europe using a trenching experiment. We recorded the abundance of soil animal taxa varying in body size (micro-, meso-, and macrofauna) 1 and 3 years after root trenching, and quantified changes in biomass, species composition, and trophic shift using stable isotopes and NLFA analysis. Among the microfauna groups studied (trophic groups of Nematoda) only the abundance of plant feeding nematodes showed a trend in being decreased by -58% due to root trenching. Major soil mesofauna groups, including Collembola and Oribatida, suffered to a similar extent from root trenching with their abundance and biomass being reduced by about 30–40%. The soil macrofauna groups studied (Diplopoda, Isopoda, Chilopoda, Araneae, Coleoptera) generally were only little affected by root trenching suggesting that they rely less on root-derived resources than micro- and in particular mesofauna. Notably, the community structure of micro-, meso-, and macrofauna was not affected by root trenching. Further, we observed trophic shifts only in 2 out of 10 investigated species with the shifts generally being only minor. The results indicate that soil animal communities are markedly resilient to deprivation of root-derived resources suggesting that links to root-derived resources are non-specific. However, this resilience appears to vary with body size, with mesofauna including both decomposers as well as predators being more sensitive to the deprivation of root-derived resources than microfauna (except for root feeders) and macrofauna. Overall, this suggests that body size constrains the channeling of energy through soil food webs, with root-derived resources in temperate forests being channeled predominantly via soil taxa of intermediate size, i.e., mesofauna.

The Kroof experiment: realization and efficacy of a recurrent drought experiment plus recovery in a beech/spruce forest

AbstractForest ecosystems play a central role in global water and carbon cycles, yet the impact of global climate change, in particular drought, on trees and forests is poorly understood. Therefore, there is an urgent need for forest‐scale experiments in improving our understanding of trees’ responses to extreme drought events and subsequent recovery under field conditions. Here, we present the design and efficacy of a novel throughfall exclusion experiment with retractable roofs in a mature forest allowing for flexible drought and recovery periods. A total of 12 plots (144 ± 26 m2 on average) with 3–7 European beech and Norway spruce trees each were established by root trenching to a depth of one meter, four years prior to the experiment. Subsequent installation of roofs (n = 6) allowed for the removal of throughfall precipitation and almost a complete non‐availability of soil water in the upper 70 cm during five subsequent growing seasons, that is, 2014–2018. This reduction in available soil water resulted in pre‐dawn leaf water potentials down to −1.8 MPa in mature trees. Stem diameter growth decreased by 30% in beech and 70% in spruce, and fine root abundance was reduced by 57% in beech and 73% in spruce compared with controls. After only one growing season, the mycorrhizal community composition changed in response to drought. Careful watering of hydrophobic forest soils in early summer of 2019 resulted in recovered pre‐dawn leaf water potentials of drought‐stressed trees within one week. Recovery of stem diameter growth, however, did not occur within the same growing season and remained reduced by 33% in beech and 69% in spruce compared with controls. The implemented throughfall exclusion system imposed recurrent seasonal drought events on a mature beech/spruce forest with high efficacy. Shifts in community composition of mycorrhizae in parallel to tree growth decline advocate for a more holistic view on forest‐scale drought and watering experiments, particularly in light of more frequently predicted drought events in future. The perennial nature of mature trees and their subsequent slow recovery from drought, that is, over multiple growing seasons, argues for more long‐term experiments that span several years.

Carbon input manipulations affecting microbial carbon metabolism in temperate forest soils – A comparative study between broadleaf and coniferous plantations

Large uncertainties exist about the relative importance of aboveground litter and root carbon input on soil organic carbon decomposition in different forest types. Here, we report on our detritus input and removal treatments conducted to investigate how changes in aboveground and belowground carbon inputs affect soil organic carbon content and various microbial carbon metabolic functions in different plantation types (oak vs. pine, broadleaf vs. coniferous). The results of our study showed that doubling aboveground litter significantly increased SOC content and labile carbon metabolism in the oak plantation but not the pine plantation. Root trenching and aboveground litter removal decreased SOC content and carbon metabolisms. The effect of root trenching on carbon metabolisms was weaker than litter removal in the oak plantation but not the pine plantation. Detritus input and removal treatments changed the diversity and function of labile carbon (starch, carbohydrates, and amines/amides) and the metabolic activity of soil microorganisms in oak plantation, but mainly influenced recalcitrant carbon (polymers) metabolism in the pine plantation. Detritus input and removal treatments influenced the composition of microbial carbon metabolic genes and functions mainly by modifying the soil environment and nutrient availability including moisture, pH, nitrate content, and available phosphorus content in the oak plantation, while it influenced carbon metabolism by altering soil moisture, and the ammonium, nitrate, and organic carbon content in the pine plantation. These findings indicate that different forest ecosystems could respond differently to different disturbances, and forest management should be adjusted accordingly.

Deprivation of root-derived resources affects microbial biomass but not community structure in litter and soil.

The input of plant leaf litter has been assumed to be the most important resource for soil organisms of forest ecosystems, but there is increasing evidence that root-derived resources may be more important. By trenching roots of trees in deciduous and coniferous forests, we cut-off the input of root-derived resources and investigated the response of microorganisms using substrate-induced respiration and phospholipid fatty acid (PLFA) analysis. After one and three years, root trenching strongly decreased microbial biomass and concentrations of PLFAs by about 20%, but the microbial community structure was little affected and the effects were similar in deciduous and coniferous forests. However, the reduction in microbial biomass varied between regions and was more pronounced in forests on limestone soils (Hainich) than in those on sandy soils (Schorfheide). Trenching also reduced microbial biomass in the litter layer but only in the Hainich after one year, whereas fungal and bacterial marker PLFAs as well as the fungal-to-plant marker ratio in litter were reduced in the Schorfheide both after one and three years. The pronounced differences between forests of the two regions suggest that root-derived resources are more important in fueling soil microorganisms of base-rich forests characterized by mull humus than in forests poor in base cations characterized by moder soils. The reduction in microbial biomass and changes in microbial community characteristics in the litter layer suggests that litter microorganisms do not exclusively rely on resources from decomposing litter but also from roots, i.e. from resources based on labile recently fixed carbon. Our results suggest that both bacteria and fungi heavily depend on root-derived resources with both suffering to a similar extent to deprivation of these resources. Further, the results indicate that the community structure of microorganisms is remarkably resistant to changes in resource supply and adapts quickly to new conditions irrespective of tree species composition and forest management.

Effect of organic matter manipulation on the seasonal variations in microbial composition and enzyme activities in a subtropical forest of China

Purpose The aim of this study was to determine the impacts of reduced aboveground and belowground C inputs on the community composition of soil microbes and enzyme activities in a seasonal context. Materials and methods Litterfall removal, root exclusion, and stem girdling treatments under a subtropical conifer plantation growing on a coarse texture of sandy soil in southeast China were employed. One year after the initiation of the treatments, we measured the soil microbial biomass, community composition, and enzyme activities, including hydrolytic and oxidative extracellular enzymes on a seasonal basis. Soil inorganic N, dissolved organic C and N, and available P were also determined. Results and discussion Seasonal variations of soil microbial composition and enzyme activities were attributed to soil temperature and moisture and soil nutrient availability. Girdling treatments significantly increased the abundances of gram-negative bacteria and actinomycetes in winter when soil temperature, moisture, and available nutrients were at the lowest level among the four seasons. Girdling alone and girdling combined with litter removal and root trenching significantly decreased the cellobiohydrolase, β-glucosidase, β-1,4-N-acetylglucosaminidase, and acid phosphatase activities in autumn. These hydrolytic enzyme activities were significantly correlated with soil moisture, NH4+, DOC, and available P. We also found a significant relationship between hydrolytic enzyme activities and the ratio of gram-positive to gram-negative bacteria. Conclusions Plant belowground C allocation, soil temperature, and moisture drove the seasonal patterns of soil microbial composition and enzyme activities. Labile C input by root exudates is a key determinant of ecosystem functions mediated by soil microbes such as microbial decomposition processes.

Stored root carbohydrates can maintain root respiration for extended periods.

Tight coupling between below-ground autotrophic respiration and the availability of recently assimilated carbon (C) has become a paradigm in the ecophysiological literature. Here, we show that stored carbohydrates can decouple respiration from assimilation for prolonged periods by mobilizing reserves from transport roots to absorptive roots. We permanently disrupted the below-ground transfer of recently assimilated C using stem girdling and root trenching and measured soil CO2 efflux for over 1 yr in longleaf pine (Pinus palustris), a species that has large reserves of stored carbohydrates in roots. Soil CO2 efflux was not influenced by girdling or trenching through the 14-month observation period. Stored carbohydrate concentrations in absorptive roots were not affected by the disrupted supply of current photosynthate for over 1 yr; however, carbohydrate concentrations in transport roots decreased. Our results indicate that root respiration can be decoupled from recent canopy assimilation and that stored carbohydrates can be mobilized from transport roots to absorptive roots to maintain respiration for over 1 yr. This refines the current paradigm that canopy assimilation and below-ground respiration are tightly coupled and provides evidence of the mechanism and dynamics responsible for decoupling the above- and below-ground processes.

Tree seedlings respond to both light and soil nutrients in a Patagonian evergreen-deciduous forest

Seedlings of co-occurring species vary in their response to resource availability and this has implications for the conservation and management of forests. Differential shade-tolerance is thought to influence seedling performance in mixed Nothofagus betuloides–Nothofagus pumilio forests of Patagonia. However, these species also vary in their soil nutrient requirements. To determine the effects of light and soil nutrient resources on small seedlings we examined responses to an experimental reduction in canopy tree root competition through root trenching and restricting soil nutrient depletion through the addition of fertilizer. To understand the effect of light these treatments were undertaken in small canopy gaps and nearby beneath undisturbed canopy with lower light levels. Seedling diameter growth was greater for N. pumilio and height growth was greater for N. betuloides. Overall, diameter and height growth were greater in canopy gaps than beneath undisturbed canopy. Such growths were also greater with fertilizer and root trenching treatments, even beneath undisturbed canopy. Seedling survival was lower under such treatments, potentially reflecting thinning facilitated by resource induced growth. Finally, above-ground biomass did not vary among species although the less shade tolerant N. pumilio had higher below-ground biomass and root to shoot biomass ratio than the more shade tolerant N. betuloides. Above- and below-ground biomass were higher in canopy gaps so that the root to shoot biomass ratio was similar to that beneath undisturbed canopy. Above-ground biomass was also higher with fertilizer and root trenching treatments and that lowered the root to shoot biomass ratio. Restricting soil nutrient depletion allowed seedlings of both species to focus their responses above-ground. Our results support a view that soil nutrient resources, as well as the more commonly studied light resources, are important to seedlings of Nothofagus species occurring on infertile soils.

Aboveground and belowground litter have equal contributions to soil CO2 emission: an evidence from a 4-year measurement in a subtropical forest

Changing quantity and quality of plant C input to soils under global change influences soil C cycling in terrestrial ecosystems. However, how soil CO2 emission responds to changes in C input remains poorly understood. A detritus input and removal experiment was conducted in a subtropical forest (Cunninghamia lanceolata) to investigate how aboveground and belowground litters affect soil respiration (RSoil). In this experiment, four treatments with three replicates were included, as follows: control (CK), litter removal (NL), root trenching (NR), and no C-input (i.e. litter removal combined with root trenching, NI). RSoil was measured for 4 years from 2011 to 2014. The mean annual CO2 effluxes in the NL, NR, and NI plots were lower (23.4%, 24.9%, and 38.8%, respectively) than those in the CK plots, suggesting that decreasing C input significantly decreased RSoil. Soil heterotrophic respiration (soil organic matter decomposed by microorganisms) accounted for 52.1% of RSoil, and aboveground recent litter decomposition and belowground autotrophic respiration (live roots and associated microorganism) contributed to 23.7% and 24.2% of RSoil, respectively. RSoil was significantly and positively correlated with soil temperature, but negatively correlated with volumetric soil moisture. The variation in RSoil was more explained by soil temperature than soil moisture, and the responses of RSoil to soil temperature and moisture were altered by C input manipulation. Annual RSoil rate was strongly and negatively related to the Gram-positive bacteria concentration and the ratio of Gram-positive to -negative bacteria. This study highlighted that aboveground recent leaf litter and belowground live roots and associated microbes had similar contributions to RSoil, and soil temperature and Gram-positive bacteria were the dominant factors controlling RSoil in a subtropical forest.

Effects of litter and root exclusion on soil microbial community composition and function of four plantations in subtropical sandy coastal plain area, China

We conducted detritus input and removal treatment (DIRT) to examine the effects of shifting above- and belowground carbon (C) inputs on soil microbial biomass, community composition and function in subtropical Pinus elliottii, Eucalyptus urophylla × Eucalyptus grandis, Acacia aulacocarpa and Casuarina equisetifolia coastal sandy plain forests, and the treatments included: root trenching, litter removal and control. Up to September 2015, one year after the experiment began, we collected the 0-10 cm soil samples from each plot. Phospholipid fatty acid (PLFA) analysis was used to characterize the microbial community composition, and micro-hole enzymatic detection technology was utilized to determine the activity of six kinds of soil enzymes. Results showed that changes in microbial biomass induced by the C input manipulations differed among tree species, and mainly affected by litter and root qualily. In E. urophylla × E. grandis stands, root trenching significantly decreased the contents of total PLFAs, Gram-positive bacteria, Gram-negative bacteria, fungi and actinomycetes by 31%, 30%, 32%, 36% and 26%, respectively. Litter removal reduced the contents of Gram-positive bacteria, fungi and actinomycetes by 24%, 27% and 24%, respectively. However, C input manipulations had no significant effect on soil microbial biomassunder other three plantations. According to the effect of C input manipulations on soil microbial community structure, litter and root exclusion decreased fungi abundance and increased actinomycetes abundance. Different treatments under different plantations resulted in various soil enzyme activities. Litter removal significantly decreased the activities of cellobiohydrolase, β-glucosidase, acid phosphatase and N-acetyl-β-d-glucosaminidase of P. elliottii, A. aulacocarpa and C. equisetifolia, root exclusion only decreased and increased the activities of β-glucosidase in P. elliottii and A. aulacocarpa forest soils, respectively. Litter removal also decreased the activities of polyphenol oxidase (PPO) and peroxidase (PER) in P. elliottii and C. equisetifolia forest soils, while root trenching had no significant effect on the activities of PPO and PER under all plantations. The properties of litter and root were the important factors in determining the soil microbial community and enzyme activity, and the change of soil microenvironment, such as temperature and moisture, caused by C input manipulations was also the important driver for the change of soil microbial property.

Constrained partitioning of autotrophic and heterotrophic respiration reduces model uncertainties of forest ecosystem carbon fluxes but not stocks

AbstractWe partitioned the soil carbon dioxide flux (Rs) into its respective autotrophic and heterotrophic components in a mature temperate‐boreal forest (Howland Forest in Maine, USA). We combined automated chamber measurements of Rs with two different partitioning methods: (1) a classic root trenching experiment and (2) a radiocarbon (14C) mass balance approach. With a model‐data fusion approach, we used these data to constrain a parsimonious ecosystem model (FöBAAR), and we investigated differences in modeled C fluxes and pools under both current and future climate scenarios. The trenching experiment indicated that heterotrophic respiration accounted for 53 ± 11% of total Rs. In comparison, using the 14C method, the heterotrophic contribution was 42 ± 9%. For both current and future model runs, incorporating the partitioning data as constraints substantially reduced the uncertainties of autotrophic and heterotrophic respiration fluxes. Moreover, with best fit model parameters, the two partitioning methods yielded fundamentally different estimates of the relative contributions of autotrophic and heterotrophic respiration to total Rs, especially at the annual time scale. Surprisingly, however, modeled soil C and biomass C pool size trajectories did not differ significantly between model runs based on the different methods. Instead, model differences in partitioning were compensated for by changes in C allocation, resulting in similar, but still highly uncertain, soil C pool trajectories. Our findings show that incorporating constraints on the partitioning of Rs can reduce model uncertainties of fluxes but not pools, and the results are sensitive to the partitioning method used.

Tree diameter growth after root trenching in a mature mixed stand of Norway spruce (Picea abies [L.] Karst) and European beech (Fagus sylvatica [L.

Key message Root trenching of Norway spruce and European beech caused no long-term decrease of stem growth and only temporal growth reductions in European beech.

Clear‐cutting and slash burning effects on soil CO2 efflux partitioning in Chinese fir and evergreen broadleaved forests in subtropical China

AbstractClear‐cutting (CC) and slash burning (SB) are common silvicultural practices in subtropical China, yet the time‐course response of soil CO2 efflux components to such disturbance is not well understood. This study examined the effects of CC and SB on soil CO2 efflux components in a Cunninghamia lanceolata (Lamb.) Hook (Chinese fir, CF) plantation and a secondary evergreen broadleaved forest (BF) located in Fujian Province, southeastern China. Aboveground litter removal and root trenching were used to estimate CO2 fluxes from soil organic matter decomposition (RSOM), litter decomposition (RL), and autotrophic respiration by roots and mycorrhizae (RR). These components were measured 5–7 times per month from 18 October 2001 to 25 December 2003 using soda lime absorption. We found that RR, RL and RSOM were initially higher in CC and SB plots than controls in both forests, but these three component fluxes in disturbed plots all fell below those of the control 5–20 months after the disturbance. Also, Q10 values of these components decreased following disturbance. The annual flux of each respiration component was greater under BF than CF. The contribution of RR to soil CO2 efflux in the control plots averaged 35% in CF and 46% in BF. RSOM was the dominant component of soil CO2 efflux in CC and SB plots, accounting for over 50%. Our results highlight the importance of temporal trends of the component fluxes following disturbance and contribute to a broader understanding of forest management effects on the soil C cycle.

改变碳输入对亚热带人工林土壤微生物生物量和群落组成的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 改变碳输入对亚热带人工林土壤微生物生物量和群落组成的影响 DOI: 10.5846/stxb201310142473 作者: 作者单位: 1,福建师范大学地理科学学院 作者简介: 通讯作者: 中图分类号: S718.5 基金项目: 国家自然科学基金项目(41371269);教育部新世纪优秀人才支持计划(DB-168);福建省杰出青年科学基金项目(2060203) Changes of above- and belowground carbon input affected soil microbial biomass and community composition in two tree species plantations in subtropical China Author: Affiliation: College of Geographical Sciences, Fujian Normal University 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:通过在亚热带杉木(Cunninghamia lanceolata)和米老排(Mytilaria laosensis)人工林中设置互换凋落物、去除凋落物、去除凋落物+去除根系和对照处理来分析改变地上、地下碳输入对人工林土壤微生物生物量和群落组成的影响。结果显示,改变地上、地下碳输入对土壤微生物生物量碳、氮的影响因树种而异。在米老排林中,土壤微生物生物量不受碳源的限制。而在杉木林中,加入米老排凋落物、去除凋落物和去除凋落物+去除根系3种处理中土壤微生物生物量碳、氮具有明显增加的趋势。磷脂脂肪酸分析结果显示,杉木林中,添加高质量的米老排凋落物后,革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了24%、24%、53%、25%、28%,革兰氏阴性细菌和丛枝菌根真菌的相对丰度均有显著增加。与对照相比,杉木林中去除凋落物后革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了22%、29%、44%、25%、52%,真菌与细菌比值显著增加了21%。但是,去除凋落物+去除根系处理对两个树种人工林土壤微生物群落组成均无显著影响。米老排和杉木林土壤微生物生物量碳、氮的季节变化格局不同,土壤养分有效性可能是驱动土壤微生物生物量季节变化的主要因子。未来研究需要关注凋落物和根系在不同树种人工林中对土壤微生物群落的相对贡献。 Abstract:We employed Detritus Input and Removal Experiment (DIRT) to examine the effects of carbon (C) input on soil microbial biomass and community composition in 19-year-old Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) and Mytilaria laosensis forests in subtropical China. The treatments included:(1) reciprocal litter transplant; (2) litter removal; (3) no inputs (litter removal+ root trenching); and (4) control. Each treatment had four 2 m×2 m plots. From January to December 2012, we collected the top 5 cm soil layer samples monthly from C. lanceolata and M. laosensis plots. Chloroform fumigation-extraction was used to determine the soil microbial biomass C and nitrogen (N) contents. Phospholipid fatty acid (PLFA) analysis was used to characterize the microbial community composition in soil samples collected in June 2012. Results suggested that the C input manipulations induced differences in soil microbial biomass and community composition were dependent on tree species. C input manipulations had no significant effects on soil microbial biomass C and N under M. laosensis. However, the concentrations of microbial biomass C and N seemed to increase under C. lanceolata. PLFA analysis showed that M. laosensis litter significantly increased the contents of bacterial PLFAs, fungal PLFAs and actinomycetes, and significantly enhanced the percent abundance of gram-negative bacteria and arbuscular mycorrhizal fungi under C. lanceolata. Litter removal significantly increased the contents of gram-positive bacteria, gram-negative bacteria, arbuscular mycorrhizal fungi, actinomycetes and fungi by 22%, 29%, 44%, 25% and 52%, respectively, and also increased the fungi to bacteria ratio by 21% compared with the control in C. lanceolata soil. However, litter removal and root trenching did not change soil microbial community composition in C. lanceolata and M. laosensis soils. Seasonal patterns of microbial biomass C and N were different between C. lanceolata and M. laosensis plantations. Nutrient availability rather than soil temperature, moisture or fresh litter input, may determine seasonal fluctuation of soil microbial biomass in this study. Our results suggested that further studies are required to confirm the relative contribution of above- and belowground C inputs in different tree species plantations in subtropical China. 参考文献 相似文献 引证文献

Effects of manipulated above- and belowground organic matter input on soil respiration in a Chinese pine plantation.

Alteration in the amount of soil organic matter input can have profound effect on carbon dynamics in forest soils. The objective of our research was to determine the response in soil respiration to above- and belowground organic matter manipulation in a Chinese pine (Pinus tabulaeformis) plantation. Five organic matter treatments were applied during a 2-year experiment: both litter removal and root trenching (LRRT), only litter removal (LR), control (CK), only root trenching (RT) and litter addition (LA). We found that either aboveground litter removal or root trenching decreased soil respiration. On average, soil respiration rate was significantly decreased in the LRRT treatment, by about 38.93% ± 2.01% compared to the control. Soil respiration rate in the LR treatment was 30.65% ± 1.87% and in the RT treatment 17.65% ± 1.95% lower than in the control. Litter addition significantly increased soil respiration rate by about 25.82% ± 2.44% compared to the control. Soil temperature and soil moisture were the main factors affecting seasonal variation in soil respiration. Up to the 59.7% to 82.9% seasonal variation in soil respiration is explained by integrating soil temperature and soil moisture within each of the various organic matter treatments. The temperature sensitivity parameter, Q 10, was higher in the RT (2.72) and LA (3.19) treatments relative to the control (2.51), but lower in the LRRT (1.52) and LR treatments (1.36). Our data suggest that manipulation of soil organic matter input can not only alter soil CO2 efflux, but also have profound effect on the temperature sensitivity of organic carbon decomposition in a temperate pine forest.