Changes In Soil Nutrient Availability Research Articles

Post-fire Effects on Soil Properties in High altitude Mixed-conifer Forest of Nepal

Studies on the effects of wildfires on soil are common in mixed-conifer forests worldwide; however, such studies are less frequent in the context of high-altitude mixed-conifer forests. In this research, we analyzed the soil physicochemical properties 14 years after a high-intensity wildfire. Soil samples were collected from a depth of 0–10 cm across 100 composite samples, representing both control and burnt areas. Our findings revealed significant changes in soil characteristics in the burnt area compared to the control area. Specifically, the average soil pH, electrical conductivity, and available potassium increased by 3 %, 81 %, and 53 %, respectively, in the burnt area, while available phosphorus decreased by 6 %. Conversely, the average total nitrogen and organic matter showed non-significant decreases of 20 % and 12 % in the burnt area compared to the control area. No significant differences were found in slope aspects. Electrical conductivity and available potassium varied significantly among upper (3300–3500 m), middle (3100–3300 m), and lower (2900–3100 m) altitude ranges. Principal component analysis explained a total of 50.1 % of the variance, with approximately 27.4 % explained by the first axis and 22.7 % by the second axis. The control and burnt areas were closely clustered, indicating similar soil properties. Electrical conductivity, available potassium, and pH were more linked to the burnt forests, while nitrogen and organic matter were more associated with the control forests. Consequently, post-fire restoration efforts should consider potential changes in soil nutrient availability to facilitate successful vegetation recovery. This study enhances the formulation of more precise post-fire land management strategies, improves forest restoration initiatives, and promotes sustainable land-use practices by comparing unburnt natural forests.

Canopy gap impacts on soil organic carbon and nutrient dynamic: a meta-analysis

Key messageThe forest canopy gaps, formed by natural or anthropogenic factors, have been found to reduce soil carbon content and increase nutrient availability. The magnitudes of these effects have been observed to increase with gap age and size, and are largely influenced by changes in temperature, precipitation, and solar radiation.ContextLocal studies have illustrated the influence of canopy gaps on the spatial heterogeneity of soil carbon and nutrients, playing a pivotal role in driving forest regeneration and succession. Nevertheless, it remains largely unknown whether the response of soil carbon and nutrient content to gap formation is consistent across forest ecosystems at global scale.AimsThe aim of this paper is to assess the homogeneity of the observed responses of soil carbon and nutrients following gap formation among a wide array of forest ecosystems and climatic regions.MethodsWe performed a meta-analysis synthesizing 2127 pairwise observations from 52 published articles to quantify the changes in in soil physical, chemical, and microbial variables resulting from gap creation in natural forests and plantations spanning tropical to boreal regions.ResultsCanopy gaps resulted in significant decrease of soil organic carbon (Corg) and microbial carbon (Cmic). The concentrations of ammonium (NH4+), nitrate (NO3−), and available phosphorus (available P) increased following gap creation. These changes mainly occurred in the growing season and in the mineral soil layer, becoming more pronounced with increasing gap age and size. The change in Corg was negatively regulated by mean annual precipitation, and was associated with the changes in Nt and Nmic. The change in NH4+ was positively regulated by mean annual temperature, and was associated with the changes in available P and oxidoreductases (Ox-EEAs). The model explaining the change in soil carbon content exhibited a higher explanatory power than the one accounting for changes in soil nutrient availability.ConclusionThe results indicated that forest canopy gaps resulted in a reduction in soil carbon content and an increase in nutrient availability. These findings contribute to a better understanding of the role of small-scale disturbances as drivers of forest ecosystem succession.

Microbial nutrient limitation along a 2-million-year dune chronosequence

Long-term ecosystem development is characterized by a switch from nitrogen (N) to phosphorus (P) limitation of plant communities as soils age, which leads to changes in plant biomass, diversity, and foliar nutrient concentrations. Similar effects occur belowground, although the extent to which nutrient availability is the primary driver of long-term changes in soil microbial communities remains uncertain. To investigate this, we assessed proxies for soil microbial nutrient limitation along the Jurien Bay dune chronosequence in Western Australia, where a long-term decline in P availability is reflected in strong variation in plant and microbial community composition over 2 million years of soil development. We quantified carbon (C), N, and P in the soil microbial biomass, assayed soil enzymes involved in the acquisition of those nutrients from soil organic matter, and used microbial stoichiometric ratios and vector analysis of enzyme activities to assess whether long-term changes in soil nutrient availability are reflected in nutrient demand by soil microbes. Concentrations of microbial nutrients peaked in Holocene soils (1–6.5 ky), although differences in microbial P were not significant. There were no significant differences in microbial nutrient ratios (C:N, C:P, and N:P) along the chronosequence. Acid phosphatase activity increased continually throughout the chronosequence, while the activities of leucine aminopeptidase and β-glucosidase were greatest in Holocene soils and declined with increasing soil age. Corresponding vector lengths indicated greater investment in C-degrading enzymes in Holocene soils (≤6.5 ky), while vector angles indicated greater investment in the acquisition of P compared with N in Pleistocene soils (≥120 ky). Overall, these findings show that changes in nutrient availability during long-term pedogenesis at Jurien Bay are reflected in microbial investment in nutrient acquisition, but that the soil microbial biomass exhibits a remarkable degree of homeostasis despite major shifts in nutrient availability and community composition over 2 million years of ecosystem development.

Effects of snow removal on seasonal dynamics of soil bacterial community and enzyme activity

High latitude regions are experiencing considerable winter climate change, and reduced snowpack will likely affect soil microbial communities and their function, ultimately altering microbial-mediated biogeochemical cycles. However, the current knowledge on the responses of soil microorganisms to snow cover changes in permafrost ecosystems remains limited. Here, we conducted a 2-year (six periods) snow manipulation experiment comprising ambient snow and snow removal treatments with three replications of each treatment to explore the immediate and legacy effects of snow removal on soil bacterial community and enzyme activity in secondary Betula platyphylla forests in the permafrost region of the Daxing'an Mountains. Generally, bacterial community diversity was not particularly sensitive to the snow removal. Seasonal fluctuations in the relative abundance of dominated bacterial taxa were observed, but snow removal merely exerted a significant impact on the bacterial community structure during the snow melting period and early vegetation growing season within two consecutive years, with a reduction in the relative abundance of Chloroflexi and an increase in the relative abundance of Actinobacteria, and no evidence of cross-season legacy effects was found. Moreover, snow removal significantly altered the soil enzyme activities in the snow stabilization period and snow melting period, with an increase in soil acid phosphatase (ACP) activity of snow melting period and a decrease in polyphenol oxidase (PPO) activity of snow stabilization period as well as β-glucosidase (BG) activity of snow stabilization period and snow melting period, but this effect did not persist into the vegetation growing periods. The seasonal variations in bacterial community and enzyme activity were mostly driven by changes in soil nutrient availability. Overall, our results suggest that soil bacterial communities have rather high resilience and rapid adaptability to snow cover changes in the forest ecosystems in the cold region of the Daxing'an Mountains.

Streamflow decreases in response to acid deposition in a subtropical forest watershed in China

Streamflow reductions have been attributed to the impacts of soil nutrient availability on plant transpiration, connecting soil biogeochemical and hydrological processes. Here we conducted a plot-scale acid addition experiment and monitored long-term hydrology in a subtropical watershed to provide direct evidence for the underlying mechanisms of these connections. These results showed that acid deposition enhanced plant growth and thus increased plant transpiration in the early treatment period. It indicates that plants can increase their transport of water and nutrients to satisfy physiological demands under continuous acid deposition. Acid deposition mainly contributed to increased evapotranspiration and decreased streamflow at the watershed scale. These results provide complementary evidence of plants adjusting to acid deposition-induced changes in soil nutrient availability and these acclimations result in streamflow reductions at the watershed scale. Our results call for integrating forest biogeochemical feedback into watershed hydrology.

New Insights from Soil Microorganisms for Sustainable Double Rice-Cropping System with 37-Year Manure Fertilization

Long-term intensive use of mineral fertilizers in double rice-cropping systems has led to soil acidification and soil degradation. Manure fertilization was suggested as an alternative strategy to mitigate soil degradation. However, the effects of long-term mineral and manure fertilization on rice grain yield, yield stability, soil organic carbon (SOC) content, soil total nitrogen (TN) content, and the underlying mechanisms are unclear. Based on a long-term experiment established in 1981 in southern China, we compared four treatments: no fertilizer application (Control); application of nitrogen–phosphorus–potassium (NPK); NPK plus green manure in early rice (M1); and M1 plus farmyard manure in late rice and rice straw return in winter (M2). Our results showed that 37 years of NPK, M1, and M2 significantly increased rice grain yield by 54%, 46%, and 72%, and yield stability by 22%, 17%, and 9%, respectively. M1 and M2 significantly increased SOC content by 39% and 23% compared to Control, respectively, whereas there was no difference between Control and NPK. Regarding soil TN content, it was significantly increased by 8%, 46%, and 20% by NPK, M1, and M2, respectively. In addition, M2 significantly increased bacterial OTU richness by 68%, Chao1 index by 79%, and altered the bacterial community composition. Changes in soil nutrient availability and bacterial Simpson index were positively correlated with the changes in grain yield, while shifts in bacterial community were closely related to yield stability. This study provides pioneer comprehensive assessments of the simultaneous responses of grain yield, yield stability, SOC and TN content, nutrient availability, and bacterial community composition to long-term mineral and manure fertilization in a double rice-cropping system. Altogether, this study spanning nearly four decades provides new perspectives for developing sustainable yet intensive rice cultivation to meet growing global demands.

High adaptability of Pinus sylvestris var. mongolica to drought-induced soil nutrient deficiency

Abstract Background Drought can exert a profound influence on soil nutrient availability, and understanding whether and how tree species adapt to this change is a critical priority for predicting the consequence of climate change on forest structure and function. The objective of this study was to examine the adaptability of Mongolian pine (Pinus sylvestris var. mongolica) to drought-induced changes in soil nutrient availability from the perspective of root functions. Methods We conducted a 7-year precipitation manipulation experiment with three levels of throughfall reduction (0%, 30%, and 50%) to simulate different drought intensities. We measured soil physicochemical properties and fine-root nutrient concentrations and biomass, and calculated the stoichiometric homeostatic regulation coefficient (1/H) of fine roots. Results Drought reduced soil organic carbon (C), nitrogen (N), phosphorous (P) and inorganic N concentrations, as well as ratios of total N to total P, and available N to available P in the 0–20 cm soil layer. In contrast, drought had no significant effect on fine-root N and P concentrations, and fine-root biomass in the 0–40 cm soil layer. Fine roots displayed high homeostatic regulation coefficients of N (with 1/H values of 0.19 and 0) and P (with 1/H values of 0.33 and 0) concentrations in 0–20 and 20–40 cm soil layers, respectively. Conclusions Our results indicate that drought leads to soil nutrient deficiency and the decoupling between N and P cycling, and provide evidence that Mongolian pine has high adaptability to drought-induced decrease in soil nutrient availability by maintaining great fine-root biomass to ensure sufficient nutrient uptake.

Soil microbial communities are driven by the declining availability of cations and phosphorus during ecosystem retrogression

Development of soil microbial communities is driven by local abiotic and biotic conditions, yet our current understanding of their ecology is limited to studies in modified or young and relatively fertile ecosystems. In nutrient-impoverished soils, microbial communities may be predominantly structured by availability of key elements such as phosphorus (P) or nitrogen, regardless of the taxa (bacteria, archaea or fungi). Here, we determined if shifts in bacterial communities and biomass occurred along a long-term soil chronosequence in south-western Australia, and whether such shifts were related to changes in soil nutrient availability along the retrogressive phase of this chronosequence. We quantified shifts in the biomass and abundance of major soil microbial groups using phospholipid fatty acids and quantitative polymerase chain reaction. We found that declining soil P availability limited microbial growth and community structure. Common cations, notably magnesium, showed strong relationships with the abundance of most bacterial and archaeal taxa. In the oldest most severely impoverished soils, the fungal to bacteria ratio was higher than in the young soils, indicating fungi are better adapted to such environments. Finally, archaeal copy numbers decreased more strongly than bacterial copy numbers with increasing nutrient-impoverishment of soils. The study enhances our understanding of the ecology of soil bacteria, archaea, and fungi during ecosystem development and retrogression.

Response of foliar mineral nutrients to long‐term nitrogen and phosphorus addition in a tropical forest

Abstract Mineral nutrients play a pivotal role in plant growth, development and reproduction. The uptake and distribution of nutrients are generally limited by soil nutrient availability, affected by global change. However, the responses of foliar mineral nutrient concentrations to changes in soil nutrient availability remain largely untested in tropical forests. We used a field‐based experiment with nitrogen (N) and phosphorus (P) addition in a tropical forest in southern China to investigate the effect of N and P fertilization on exchangeable soil and foliar mineral nutrients of five understorey species. Our results show that N addition did not change soil pH, but reduced exchangeable soil Ca2+, Mg2+, Zn2+, Fe3+ and Mn2+ concentrations. In contrast, P addition increased soil pH, while it had no effects on exchangeable cations. Nitrogen addition significantly decreased foliar [Ca], [Mg] and [Mn], while P addition markedly reduced foliar [Cu] for most of the studied species. Foliar [K] and [Fe] were not affected by fertilization. The results indicate that long‐term N addition reduced the concentrations of several mineral nutrients in leaves, and we did not observe any adaptive mechanisms (e.g. increased transpiration to take up mobile soil nutrients) in the studied species to maintain foliar nutrient concentrations at high N supply. Synthesis. The responses of other foliar nutrient concentrations to N and P co‐addition were more complicated than those of N and/or P, and the specific decreases in mineral nutrient concentrations following long‐term N addition may influence key physiological process in the studied tropical understorey species, and ultimately reduce their fitness and survival under high N deposition. A free Plain Language Summary can be found within the Supporting Information of this article.

Restoration effects of fertilization and grazing exclusion on different degraded alpine grasslands: Evidence from a 10-year experiment

Understanding the changes in vegetation parameters and soil nutrients in different stages of recovery is crucial for assessing and restoring degraded grasslands. Different degraded grasslands may respond differently to fertilization and grazing exclusion due to the change in species composition, while research in this aspect is still lacking. Two lightly (LD) and one heavily degraded (HD) plots were set up, with one LD plot under grazing exclusion (LDGE), aiming to investigate the effects of these management measures on forage restoration under different degraded alpine grasslands. Nitrogen (N) addition showed a tendency to reduce community cover and aboveground biomass in LD plot, but had no effect in LDGE and HD plots. N and phosphorus (P) combined additions (N + P additions) greatly enhanced the community cover and aboveground biomass, suggesting P addition can reverse the negative effects of N addition. In LDGE plot, all fertilization treatments enhanced the growth of palatable species, and only N + P additions increased it in LD plot, while fertilization did not improve palatable species in HD plot. Additionally, grazing exclusion promoted fertilization effects, and the effects of fertilization on palatable species were much more pronounced in LDGE plot than those in LD plot. The effects of nutritious enrichment were primarily controlled by soil pH change, while they were also regulated by the changes in soil nutrient availability in LD plot. These results suggest that grazing exclusion and fertilization (especially N + P additions) can additively enhance community production of the lightly degraded alpine grasslands, while the structure of heavily degraded alpine grasslands cannot be restored by nutrition enrichment due to the forbs-dominated structure although plant production was greatly enhanced, and other measures should be combined to restore the community structure in heavily degraded alpine grasslands.

Nutrient‐use strategy and not competition determines native and invasive species response to changes in soil nutrient availability

Non‐native invasive plants often outcompete native species under high resource availability. Restoration techniques that lower resources may, therefore, create favorable conditions for resource conservative native species over resource exploitative invasive species. Research on this topic has focused on temperate grass and forb‐dominated ecosystems and has rarely been tested for woody species or tropical vegetation. We evaluated growth, resource‐use efficiency (RUE), ecophysiology, and competition (i.e. a relative interaction index based on biomass) of four woody native and two dominant invasive species from Hawaiian wet and dry tropical ecosystems in a greenhouse experiment. Density of plants was constant and species were grown with either a conspecific or the invasive species from that ecosystem type across a gradient of soil nutrient availability. Instantaneous photosynthetic rates varied minimally across nutrient availability. However, both invasive and one native species increased leaf area as nutrients increased, providing more photosynthetic area and increasing total biomass. Nitrogen RUE decreased with increasing nutrient availability for all but one native species, while phosphorus RUE remained constant for all but one native species. Competitive interactions were weak, variable, and not significantly impacted by soil nutrients. Overall, plants categorized as invasive or resource exploitative had larger changes in response variables with increasing soil nutrients compared to those categorized as native or resource conservative. These results suggest that manipulating soil nutrient availability is a potentially viable restoration tool for at least some woody species in tropical ecosystems. However, predicting restoration success requires understanding species‐specific ecophysiological traits determining response to altered environmental conditions.

Enzyme stoichiometry evidence revealed that five years nitrogen addition exacerbated the carbon and phosphorus limitation of soil microorganisms in a Phyllostachys pubescens forest.

The activity and stoichiometry of soil extracellular enzyme can provide a good indication for changes in soil nutrient availability and microbial demands for nutrients. However, it remains unclear how would nitrogen (N) deposition affect nutrient limitation of microbes in subtropical forest soils. We conducted a 5 years N addition experiment in a subtropical Phyllostachys pubescens forest. The soil nutrients and enzyme activities associated with carbon (C), N, and phosphorus (P) cycles were measured. We also examined the nutrient distribution of microorganisms using enzyme stoichiometry and vector analysis. The results showed that N addition significantly decreased the contents of soil soluble organic C and available P and increased that of available N. Furthermore, N addition significantly decreased β-N-acetyl-glucosaminidase (NAG) activity and NAG/ microbial biomass carbon (MBC), and increased acid phosphatase (ACP) and ACP/MBC. The low and moderate N addition levels significantly increased enzyme C/P, vector length, and vector angle, but significantly decreased enzyme N/P. Results of redundancy analysis showed that the change in soil enzyme activity and enzymatic stoichiometry were mainly driven by soil available P content under N addition. In summary, N addition altered the microbial nutrient acquisition strategy, which increased nutrient allocation to P-acquiring enzyme production but reduced that to N-acquiring enzyme production. Moreover, N addition exacerbated the C and P limitation of soil microorganisms. Appropriate amount of P fertilizer could be applied to improve soil fertility of subtropical P. pubescens forest in the future.

Nutrient removal by rice\u2013wheat cropping system as influenced by crop establishment techniques and fertilization options in conjunction with microbial inoculation

Nutrient uptake by the rice–wheat cropping system (RWCS) is an important indicator of soil fertility and plant nutrient status. The hypothesis of this investigation was that the rate and sources of nutrient application can differentially influence nutrient removal and soil nutrient status in different crop establishment techniques (CETs). Cropping system yield was on par in all the CETs evaluated, however, there were significant changes in soil nutrient availability and microbiological aspects. The system nitrogen (N), phosphorus (P), potassium (K) and zinc (Zn) uptake in aerobic rice system followed by zero tillage wheat (ARS-ZTW) was 15.7–17.6 kg ha−1, 0.7–0.9 kg ha−1, 7–9.8 kg ha−1 and 13.5–23.1 g ha−1 and higher than other CETs. The formulations of Anabaena sp. (CR1) + Providencia sp. (PR3) consortium (MC1) and Anabaena–Pseudomonas biofilm (MC2) recorded significantly higher values of soil chlorophyll and microbial biomass carbon and positively affected cropping system nutrient uptake and soil nutrient balance, illustrating the beneficial effect of microbial inoculation through increased supply of biologically fixed N and solubilised P. Zinc fertilization (5 kg Zn ha−1 through ZnSO4·7H2O as soil application) increased soil DTPA-extractable Zn by 4.025–4.836 g ha–1, with enhancement to the tune of 20–24% after two cropping cycles of RWCS. Our investigation recommends the need for change in the present CETs to ARS–ZTW, along with the use of microbial inoculation as a means of significantly enhancing cropping system nutrient uptake and soil nutrient status improvement.

Temperature modifies the magnitude of a plant response to Collembola presence

Soil properties and the growth and maturation of herbaceous plants are known to be influenced by the soil fauna (Collembola) and by the temperature. But little is known about how these two factors interact. We hypothesised that the vegetative and reproductive responses of Poa annua L. to the presence of soil Collembola density will change according to temperature. P. annua was grown in microcosms with or without Collembola at two different air temperature conditions, 16 °C as a Low T° vs. 19 °C as a High T°. Both factors “Collembola” and “Temperature” significantly influenced several plant and soil variables. The number of flowers, the root biomass of P. annua were higher either in presence of Collembola or under elevated temperature. The same applied for soil ergosterol or K content for example. Soil nitrate content was exclusively affected by the presence/absence of Collembola and not by the temperature. Finally, significantly interactive effects between temperature and Collembola upon several plant or soil variables (root biomass, number of flowers, soil K and Mg content) were shown. Our study suggests that biotic factors (here soil fauna) may strongly interact with climatic variables in regulating plant growth through changes in soil nutrient availability. We provide experimental evidence that climate warming modifies the effect of soil Collembola on the reproduction strategy of the plant.

Site preparation impacts on soil biotic and abiotic properties, weed control, and native grass establishment

In severely degraded systems active restoration is required to overcome legacies of past land use and to create conditions that promote the establishment of target plant communities. While our understanding of the importance of soil microbial communities in ecological restoration is growing, few studies have looked at the impacts different site preparation techniques have on these communities. We trialed four methods of site preparation: fire, top‐soil removal (TSR; removal of top 50 mm of soil), slashing (vegetation cut to 30 mm, biomass removed), and carbon (C; as sugar and saw‐dust) addition, and quantified resulting soil bacterial communities using DNA metabarcoding. We compared the effectiveness of these techniques to reduce weed biomass, improve native grass establishment, and induce changes in soil nutrient availability. TSR was the most effective technique, leading to a reduction in both available nutrients and competition from weeds. In comparison, the remaining methods had little or no effect on weed biomass, native grass establishment, or soil nutrient availability. Both TSR and C addition resulted in changes in the soil bacterial community. These changes have the potential to alter plant community assembly in many ways, such as via nutrient acquisition, pathogenic effects, nutrient cycling, and decomposition. We recommend TSR for ecological restoration of old‐fields and suggest it is a much more effective technique than burning, slashing, or C addition. Restoration practitioners should consider how their management techniques may influence the soil biota and, in turn, affect restoration outcomes.

Different responses of leaf and root traits to changes in soil nutrient availability do not converge into a community-level plant economics spectrum

Spatial heterogeneity in soil can influence the distribution of plant communities because plants differ in their ability to acquire resources. In nutrient-poor soils, plants should bear traits that prioritize conservation of resources over growth, whereas the opposite is expected in nutrient-rich soils. A coordinated response to soil fertility, in which leaves and roots converge into the same strategy, would lead to a community-level plant economics spectrum (PEScom). Here, we examine how nutrient availability across different soil types shapes the functional structure of desert shrub communities and how much of this variation is explained by species turnover or intraspecific variability (ITV). We measured leaf and root traits of 16 shrub species in four sites with contrasting soil nutrient availability in the southern edge of the Atacama Desert. In leaves, changes in soil nutrient availability were associated with a leaf economics spectrum, shifting from communities with more acquisitive strategies to communities with more conservative strategies with increasing nutrient limitation. No such pattern of co-variation was observed for roots; thus, the relationship between above and below-ground traits did not fit the PEScom. Variation of leaf traits was mainly determined by species turnover, while for root traits it was determined equally by species turnover and ITV. The lack of a PEScom appears to be related to the co-limitation of multiple resources, which promotes different responses in root traits. We highlight the importance of incorporating leaf and root traits to understand how multiple resource limitation shapes plant ecological strategies.

Plant Nitrogen and Phosphorus Resorption in Response to Varied Legume Proportions in a Restored Grassland.

An in-depth assessment of plant nutrient resorption can offer insights into understanding ecological processes and functional responses to biotic and abiotic changes in the environment. The legume proportion in a mixed grassland can drive changes in the soil environment and plant relationships, but little information is available regarding how the legume proportion influences plant nutrient resorption in mixed grasslands. In this study, three mixed communities of Leymus chinensis (Trin.) Tzvel. and Medicago sativa L. differing in legume proportion (Low-L, with 25% legume composition; Mid-L, with 50% legume composition; High-L, with 75% legume composition) were established with four replicates in a degraded grassland. Four years after establishing the mixed grassland, the quantity of biological N2 fixation by M. sativa, the availabilities of water and nitrogen (N) and phosphorus (P) in soil were examined, and the concentrations and resorption of leaf N and P for both species were measured during forage maturation and senescence. The results showed Mid-L had greater biological N2 fixation and soil N availability than Low-L and High-L, while the High-L had lower soil water and P availability, but a greater soil available N:P ratio compared with Low-L and Mid-L. Legume proportion did not alter N or P concentrations of mature leaves. However, in Mid-L N resorption was reduced by 8 to 16% for the two mixed-species compared with Low-L and High-L. High-L enhanced P resorption by 20 to 24% in both plant species compared with Low-L. The L. chinensis and M. sativa responded differently to varied legume proportion in terms of P resorption. It was concluded that legume proportion drove changes in soil nutrient availability of mixed communities, which primarily altered plant nutrient resorption during senescence, but had no influence on the nutrient concentrations of mature plants. A moderate legume proportion reduced N resorption, and increased senesced leaf N concentration of grass and legume species. The difference in P resorption by two mixed-species significantly changed the interspecific difference of senesced leaf P concentration and the N:P ratio with varied legume proportion.

Nutrient limitation of litter decomposition with long-term secondary succession: evidence from controlled laboratory experiments

Understanding ecosystem processes such as litter decomposition in response to dramatic land-use change is critical for modeling and predicting carbon (C) cycles. However, the patterns of litter decomposition along with long-term secondary succession (over 100 years) are not well reported, especially concerning nutrient limitations on litter decomposition. To clarify the response of litter decomposition to changes in soil nutrient availability, we conducted four incubation experiments involving soil and litter and nutrient addition from different successional stages and investigated the changes in microbial respiration and litter mass loss. Our results revealed that microbial respiration increased with succession without any litter addition (1.19~1.73 mg C g−1 soil), and litter addition significantly promoted microbial respiration (16.5~72.9%), especially in the early successional stage (grassland and shrubland). The decomposition rate of the same litter decreased with succession. In addition, nitrogen (N) and phosphorus (P) addition showed significant effects on litter decomposition and microbial respiration; P addition promoted litter decomposition (2.4~15.3%) and microbial respiration (10.1~34.5%) in all successional stages, while N addition promoted litter decomposition (4.0~10.3%) and microbial respiration (5.4~27.2%) in all except the last stage of succession, which showed a negative effect on litter decomposition (− 7.5%) and microbial respiration (− 6.1%), indicating possible N saturation of litter decomposition and microbial respiration. This work highlights that soil nutrient availability and successional stages need to be taken into account to predict the changes to litter decomposition in response to global changes.

Invasive lianas are drivers of and passengers to altered soil nutrient availability in urban forests

Lianas (woody vines) are a leading concern in urban forest management given their ability to reduce the growth rate and survival of trees. Efforts to control invasive lianas are widespread, yet forests are often reinvaded following management. Changes in soil nutrient availability could help explain why some forests are susceptible to reinvasion. Specifically, invasive lianas could be “drivers” of altered nutrient dynamics that persist in the soil and favor their re-establishment, or they could be “passengers” of conditions created by prior site disturbances. We test these alternative models by analyzing soils across gradients of liana cover and forest disturbance in mature hardwood forests in New York City. Overall, total non-native liana cover was linked to elevated soil pH, reduced labile carbon, and altered net potential nitrification—three conditions indicative of increased soil nutrient availability. However, the effects of lianas varied substantially by species. Non-native lianas had a positive, negative, neutral, or non-linear effect on a single soil variable depending on the species. Aggregation of total non-native liana cover can therefore obscure the direction and magnitude of species-level effects. We also found positive relationships between forest disturbance, non-native liana cover, and soil pH, but we found no relationships between disturbance and net nitrification or labile carbon. These results suggest that non-native lianas are passengers to elevated levels of disturbance and soil pH but drivers of altered carbon and nitrogen dynamics. As such, management efforts aimed at reducing soil nutrient availability and removing invasive lianas may be required to limit reinvasion and promote ecosystem recovery.

Impact of plant functional group and species removals on soil and plant nitrogen and phosphorus across a retrogressive chronosequence

Abstract In the prolonged absence of catastrophic disturbance, ecosystem retrogression occurs, which is characterized by declining soil nitrogen (N) and phosphorus (P) availability, increasing plant and soil N to P ratios, and reduced plant biomass and productivity. It is, however, largely unknown as to how the effects of plant communities on soil nutrients change during retrogression or might contribute to declining nutrient availability as retrogression proceeds. We studied a well‐characterized system of 30 lake islands in northern Sweden that collectively represent a 5,000‐year post‐fire retrogressive chronosequence. For each island, we established an experiment that involved full factorial removal of three plant functional groups (tree roots, dwarf shrubs and mosses), and of three species of dwarf shrub (Vaccinium myrtillus, V. vitis‐idaea and Empetrum hermaphroditum). After 19 years, we took various measures of soil N and P availability, and measured foliar N and P for each dwarf shrub species, for each plot in the experiment. Although plant removal effects (and particularly removal of tree roots, shrubs and Vaccinium species) on below‐ground N and P measures sometimes changed during retrogression, this seldom happened in a way that explains the decline in nutrient availability and increase in N to P ratios that characterize ecosystem retrogression. The only exceptions were that the positive effects of tree roots on soil mineral N and P, and of V. myrtillus on soil mineral P, declined during retrogression. Plant removal effects on community‐level measures of shrub N and P varied greatly across the chronosequence, but these effects again did not align with the changes in soil nutrient availability or N to P ratios that characterize ecosystem retrogression. Synthesis. Our results suggest that retrogression, and associated changes in nutrient availability and soil N to P ratios, is driven mainly by longer‐term pedogenic processes as opposed to shorter‐term effects of plant communities on soil N and P availability. More generally, they illustrate the value of long‐term and large‐scale experimental manipulations of plant communities for showing how effects of biodiversity loss on ecosystem properties vary across contrasting ecosystems.