Plant Nutrient Stoichiometry Research Articles

Temporal Precipitation Variation and Leaf Stoichiometric Changes Mediate the Dynamics of Tree Growth Responses to Nitrogen Addition Over Time

AbstractNitrogen (N) addition can stimulate tree growth; however, the strength of this growth effect usually changes over time and the factors underlying these responses are not fully understood. Based on a decade‐long N addition experiment (by adding 0, 20, 50, and 100 kg N ha−1 yr−1) in a boreal forest, we studied responses of tree growth to N addition over time and explored the potential role of temporal precipitation variation and plant stoichiometric changes in mediating this. We found positive growth responses to N addition but this effect changed nonlinearly over time. Annual precipitation was positively related to growth under high‐level N addition; hence, a hump‐shape temporal pattern in precipitation contributed to the nonlinear tree growth responses. After precipitation effects were accounted for, the positive growth responses to N addition peaked in the seventh year and then declined for all levels of N. Later reductions in growth responses could partly be attributed to increased leaf N:phosphorus (P) ratio over time, especially at higher N addition rates. We also found an increase in soil acid phosphatase, the ratio of labile to occluded soil P fraction, and a decreased ratio in leaf N to P resorption efficiency with increasing N addition rates during the late stage of this experiment, suggesting increased P demand. Collectively, our results imply that changes in plant nutrient stoichiometry with cumulative N input may limit the N stimulation on tree growth over time, while temporal precipitation variation appears unlikely to modulate this effect under the atmospheric N deposition.

Plant nutrient stoichiometry appears out of sync from soil: Increasing influences of changing climate on the grassland in inner Mongolia, China

Extremes in weather episodes seem to be the new normal. We need to better understand how changing climatic conditions alter plant growth in grasslands, especially macro nutrient uptake and stoichiometry. However, few studies have examined how warmer/colder or wetter/drier climates influence the nutrient coupling between plants and soils at the ecosystem level. Here, we investigated the changes in carbon (C), nitrogen (N), and phosphorus (P) concentrations and their stoichiometric ratios in plants and soils from 65 grassland sites along a geographic gradient in northern China. Results showed that soil C, N and P were negatively correlated with temperature and aridity. Plant N was positively correlated with temperature and aridity, but plant P was negatively correlated with temperature and aridity. Plant C had no significant relationship with either aridity or temperature. Both temperature and aridity were positively correlated with C:N, but negatively correlated with C:P and N:P in soils. The ratio of plant C:N was negatively correlated with aridity, while plant C:P was positively correlated with temperature. Plant N:P was positively correlated with temperature and aridity. Our findings imply that the often-found positive relationships between plant and soil nutrients at one site might not apply to a broad geographic scale with varying climatic conditions, likely because of the “dilution effect” and disparate plant nutrient utilization strategies. It is conceivable that rapid climate shifts and the resulting changes in element availability, turnover rates, absorption, and use efficiency might cause desynchrony of C, N, and P cycles between plants and soils.

An assessment of nutrient removal by harvesting constructed floating wetlands in two coastal lagoons in the SE Baltic Sea

AbstractIn the last decades, so‐called internal or sea‐based mitigation measures have been suggested as nature‐based solutions to remove nutrients and improve water quality in semi‐enclosed coastal waters. However, these have rarely been tested in the field, especially in colder climates where winter ice cover is common. The aim of this experimental research was to investigate plant growth conditions in such an environment, as well to estimate nutrient removal capacity by harvesting constructed floating wetlands (CFWs). We tested small (24–28 m2) CFWs (Biomatrix®, Scotland, UK) at two demonstration sites: the Curonian lagoon (CL, Lithuania) and Szczecin lagoon (SL, Poland). In the CL, CFWs were planted predominantly with Carex acutiformes (Ehrh.), while the SL CFW was planted mainly with the reed Phragmites australis (Cav.) Trin. ex Steud. We aimed to test the amount of nutrient removal by plant harvesting over three subsequent years (2019–2021). We investigated carbon storage capacity and plant nutrient stoichiometry as indicators of potential nutrient limitation in the brackish coastal waters. Plant biomass increased annually, stabilising at 2.5–3.7 kg wet weight m−2. The total nutrient uptake per installed island area varied with the plant species composition. In the successive years, the harvested plants from the CL CFW dominated by Carex accumulated 10.4–13.1 g N m−2, 0.6–0.8 g P m−2 and 318–431 g C m−2 per year. The harvest from the SL CFW dominated by Phragmites contained a two‐times higher amount of nutrients, the respective figures being 21.2 g N m−2, 1.6 g P m−2 and 704 g C m−2. The nutrient stoichiometry in the vegetation did not suggest the presence of sub‐optimal growth conditions due to nitrogen limitation. However, the CL's dissolved nutrient supply was very low during the summer cyanobacteria bloom and indicated a severe nitrogen deficiency (as reflected in the dissolved inorganic nitrogen:dissolved inorganic phosphorus [DIN:DIP] molar ratio of 6). We suggest that to maximise nutrient removal capacity, tall plants with high biomass should be selected and/or plants with fine root systems to efficiently uptake the limiting nutrient from the water.

Change in the Ecological Stoichiometry of Carex thunbergii in Response to Seasonal Dynamics and Environmental Factors in Shengjin Lake, China

Exploring the effects of environmental factors and plant physiological processes on plant nutrient stoichiometry is of great significance to understanding how wetland vegetation distributes and maintains function. However, we have a limited understanding of how the combination of plant communities and seasonality with soil physicochemical properties affects nutrient stoichiometry in wetland plants. In this study, we examined these factors in Carex thunbergii and soil across four types of plant communities dominant in the riparian zone of Shengjin Lake during the non−flooding periods of December 2020 and March 2021. In winter, the total foliar C, N, and P concentrations decreased along with an increase in plant coverage, which did not differ in spring. The C, N, C: P, and N: P of foliage significantly increased over the season, while soil C, N, C: P, and N: P significantly decreased over the season. Both in winter and spring, soil C and soil N decreased along with the increase of plant coverage. Our results suggest that both plant community and soil physicochemical properties have a significant influence on plant nutrient stoichiometry. This study improves our understanding of the seasonal dynamics of plant nutrients under different communities and soil physicochemical properties.

The patterns of N/P/K stoichiometry in the Quercus wutaishanica community among different life forms and organs and their responses to environmental factors in northern China

Nitrogen (N), phosphorus (P), and potassium (K) play an essential role in plant growth, development and reproduction. The pattern of nutrient stoichiometry across various plant organs and plant life forms can reflect the trade-off of plant growth strategies. However, there is a lack of systematic research on plant nutrient stoichiometry and the influence of environmental factors. Therefore, the main forest type Quercus wutaishanica community was considered as the object for this study and samples of different life forms (trees, shrubs, herbs) and different organs (leaves, stems, roots, seeds) were collected in northern China. First, we analyzed N/P/K stoichiometry among different organs and different life forms in the Quercus wutaishanica natural community. Second, we explored the influence of environmental factors on N/P/K stoichiometry and clarified the relative contributions of variables among different life forms. The results showed that the distributions of nutrient stoichiometry in different life forms and organs were different. As the most active organ, the content of elements in leaves was significantly higher than that in other organs. Among them, P was the main limitation in leaves and roots; N was the main limitation in stems and seeds in this area. Environmental factors had different effects on the N/P/K stoichiometry of different life forms. The nutrient stoichiometry in trees was mainly affected by topographical factors; the nutrient stoichiometry in shrubs and herbs was mainly affected by soil factors. Therefore, the differences in N, P, and K stoichiometry may be caused by the growth environment and the plant’s own adaptation strategies. All of these studies provide new insight for studying the homeostasis system within plants and communities by means of stoichiometry. This study is expected to guide the management and protection of the natural community, make the natural community give more ecological functions, and provide support for the cultivation of artificial forests in the future.

Effect of Wetland Restoration and Degradation on Nutrient Trade-Off of Carex schmidtii

Plant nutrient trade-off, a growth strategy, regulates nutrient stoichiometry, allocation and stoichiometric relationships, which is essential in revealing the stoichiometric mechanism of wetland plants under environmental fluctuations. Nonetheless, how wetland restoration and degradation affect nutrient trade-off of wetland plants was still unclear. In this study, field experiments were conducted to explore the dynamic of nutrient stoichiometry and nutrient limitation of Carex schmidtii under wetland restoration and degradation. Plant nutrient stoichiometry and stoichiometric relationships among natural (NW), restored (RW), and degraded (DW) tussock wetlands were examined. Results showed that nutrient stoichiometry of C. schmidtii was partly affected by wetland restoration and degradation, and growth stages. The N:P and N:K ratios indicated N-limitation for the growth of C. schmidtii. Robust stoichiometric scaling relationships were quantified between some plant nutrient concentrations and their ratios of C. schmidtii. Some N- and P-related scaling exponents are varied among NW, RW, and DW. PCA indicated that wetland restoration and degradation had significantly affected on the nutrient trade-offs of C. schmidtii (May∼August). Compared to NW, nutrient trade-off in RW was more similar to DW. Carex schmidtii had significant correlation between most nutrients and their ratios, and the SEM indicated that plant P and K concentrations had a high proportional contribution to plant C and N concentrations. Insights into these aspects are expected to contribute to a better understanding of nutrient trade-off of C. schmidtii under wetland restoration and degradation, providing invaluable information for the protection of C. schmidtii tussock wetlands.

Effects of nitrogen addition on leaf nutrient stoichiometry in an old‐growth boreal forest

AbstractBoreal forests have been evidenced to be highly sensitive to enhanced nitrogen (N) deposition due to prevailing N limitations, and external N inputs from atmospheric deposition are expected to alter plant nutrient stoichiometry. Previous studies have mostly focused on the dominant tree species while neglecting understory plants that often play important role in the nutrient cycles in forest ecosystems. By conducting a six‐year N‐addition experiment with four treatments of 0 (control), 20 (low N), 50 (medium N), and 100 (high N) kg N·ha−1·yr−1in a boreal forest in Northeast China, we assessed the responses of leaf nutrient stoichiometry (N, phosphorus [P], potassium [K], calcium [Ca], and magnesium [Mg]) for tree, shrubs, and grass. Although the responses of different species to N addition varied, six‐year N addition, especially the medium and high N treatments, generally increased the leaf N concentration and decreased the leaf P and Ca concentrations. As a result, the foliar N:P, N:K, N:Ca, and N:Mg ratios increased consistently across plant functional groups under the high N addition compared with the control, and the grassDeyeuxia angustifoliashowed a larger increase in its foliar N:P, N:Ca, and N:Mg than the shrubs. The leaf N concentration increased consistently with soil inorganic N in a nonlinear saturating form, while the other leaf nutrients either decreased (P, Ca) or were not affected (Mg, K) by the soil N availability. Consequently, the foliar N:P, N:K, N:Ca, and N:Mg ratios increased linearly with increasing soil N availability. In spite of this alteration of the leaf nutrient stoichiometry with increasing soil N availability, foliar nutrients and their stoichiometry were less affected under the low N treatment in both trees and understory plants, suggesting minor effects of current N deposition rates on the foliar nutrient balance in boreal forests.

Legacy effects of nitrogen deposition on plant nutrient stoichiometry in a temperate grassland

Nitrogen (N) deposition has negative consequences for plant communities and ecosystem functioning. Nitrogen deposition is declining or is projected to decline in many regions due to the reduction of N-compound emissions. It remains unknown whether the cessation of N deposition will have legacy effects on plant nutrient stoichiometry. If there are stoichiometric legacy effects at the community-level from prior N enrichment, the contribution of changes in community composition relative to the stoichiometric responses of individual functional groups in driving these changes is unknown. We measured plant N:P ratio at both functional group level and community level in a temperate steppe in three consecutive years following cessation of a 7-year N addition experiment with a wide-range of total amount added N in which the total amount of N added ranged from 0 to 350 g m−2. The total amount of N addition was positively correlated with tall rhizomatous grass productivity and negatively correlated with tall bunchgrass productivity. Plant N:P ratios at both functional group and community levels did not change across N addition gradient. Community composition shifts contributed less than intra-group variation to the total variation of community level nutrient status in response to historic N addition. Our results indicated that biological N:P imbalance in response to N deposition can be rapidly ameliorated after the cessation of N deposition. Such legacy effects of N deposition on plant nutrient status are largely driven by the changes of nutrient status of individual plants instead of N-induced shifts in community composition.

Impact of desertification on soil and plant nutrient stoichiometry in a desert grassland

Grassland degradation resulting from desertification often alters the carbon (C), nitrogen (N) and phosphorus (P) cycles within grassland ecosystems. To estimate the effects of desertification on the C, N, and P concentrations and C:N:P stoichiometry of plants and soil, we examined C, N, and P concentrations in plant tissues (leaves, roots and litter) and soil across five degrees of desertification in the desert grassland of Ningxia, China (control, light, moderate, severe and very severe desertification stages). The C, N, and P concentrations and C:N:P stoichiometry of the leaves, roots and litter differed among the different desertification stages. Desertification resulted in opposing trends between the leaf N concentration and leaf C:N ratio. With the exception of the very severe desertification stage, the leaf N:P ratio decreased over the process of grassland desertification. The soil C, N, and P concentrations and soil N:P and C:P ratios decreased significantly along the grassland desertification gradient. In contrast, the soil C:N ratio remained relatively stable during desertification (10.85 to 11.48). The results indicate that desertification is unfavourable to C and N fixation and has a negative effect on the ecosystem structure and function of desert grassland.

Soil Degradation Effects on Plant Diversity and Nutrient in Tussock Meadow Wetlands

Soil degradation, a growing problem in the arid and semi-arid area, significantly influences wetland dynamics and nutrient cycling. Using tussock wetlands as objectives, this study aims to explain the effects of long-term soil degradation on plant diversity and dominant species and identify the impacts of long-term soil degradation, growing month, species, and their interactions on plant nutrient stoichiometry in Momoge wetland. Field experiments were undertaken to explore the responses of plant diversity and nutrient to soil degradation in Momoge wetland. The relationships between plant nutrient and soil physicochemical properties were examined by canonical correspondence analysis (CCA). Soil nutrient significantly decreased in degraded tussock wetlands. Long-term soil degradation altered plant diversity and the important values of dominant species. Plant nutrient indicated that the effects of soil degradation on plant carbon, nitrogen, and phosphorus were not significant at the single species level. Furthermore, plant stoichiometric patterns were not sensitive to soil degradation. However, both the N/P ratio in soil and plants showed a nitrogen limitation for the plant growth in wetlands. The CCA indicated that the soil total nitrogen and electrical conductivity were the primary factors affecting the cycle of biogenic elements in tussock wetlands. Results highlight the differences in biogenic elements in wetland soil and vegetation and identify the significant effects of soil degradation on the wetland plants. These findings suggest that the variation of nutrient availability and electronic conductivity affects the growth of the wetland species.

Change in ecological stoichiometry of Carex brevicuspis in response to seasonal dynamics and elevation in Dongting Lake, China

Plant nutrient stoichiometry is affected by both environmental factors and plant physiological processes. However, we know little about how small elevation gradients (influencing e.g. flooding regimes) and seasonality combine with soil physicochemical properties to influence nutrient stoichiometry in wetland plants. In this study, we examined these factors in Carex brevicuspis at Dongting Lake, China, during the non‐flooding periods in March, May and December of 2015 and February of 2016. We found that total foliar C concentration increased as elevation increased, especially during December 2015 and February 2016. At the low‐elevation site, total foliar C concentration decreased over the season, whereas it first increased and then decreased over time at higher elevations. Foliar total N and P concentrations decreased from March to May and subsequently increased throughout the season, and these concentrations were always much higher at the low‐elevation site. The C:N and C:P ratios first increased and then decreased over the season, while increasing with rising elevation. The N:P ratio was lower at the low‐elevation site, especially during May 2015 and February 2016; its variation over time differed across the elevations. A canonical correspondence analysis revealed that soil organic C, total N and soil nitrate N are important for determining C. brevicuspis stoichiometry. Our results suggest that both elevation and plant life stage have a significant influence on plant stoichiometry. This study improves our understanding of the seasonal dynamics of plant nutrients under different geographical conditions.

Vegetation growth and sediment dynamics in a created freshwater wetland

Understanding how the hydrological regime in relation to sediment type interferes with ecosystem development is important when wetlands are created with soft muddy material. Especially when plants are used as ecological engineers to promote crest stability and soil formation. We carried out a two-year mesocosm experiment with sediments derived from the Dutch lake Markermeer to identify the effects of the hydrological regime and sediment type on ecosystem functioning in terms of nutrient availability. We measured plant productivity, plant nutrient stoichiometry, and concentrations of N, P, and K in shoots and roots of Phragmites australis and Rumex maritimus and monitored how the clay-rich sediment from lake Markermeer changed into a wetland soil. Plants grown on Markermeer sediments tend to be N limited when periodically inundated and P limited when not inundated at all. The P availability was determined by the hydrological regime, while the N availability was determined by both the hydrological regime and the sediment type. Ecosystem development on created wetlands can be manipulated by adequate management of the hydrological regime, as plant species respond differently to changes in nutrient availability. This should be considered in eco-engineering projects where plants are used as ecological engineers to fasten ecosystem development on wetlands that are to be created from clay-rich material.

Plant and soil nutrient stoichiometry along primary ecological successions: Is there any link?

Ecological stoichiometry suggests that plant Nitrogen (N)-to-Phosphorus (P) ratios respond to changes in both soil N:P stoichiometry and soil N and P availability. Thus we would expect that soil and plant N:P ratios be significantly related along natural gradients of soil development such as those associated with primary ecological successions. Here we explicitly search for linkages between plant and soil N:P stoichiometry along four primary successions distributed across Europe. We measured N and P content in soils and plant compartments (leaf, stem and root) of 72 wild plant species distributed along two sand dune and two glacier successions where soil age ranges from few to thousand years old. Overall we found that soil N:P ratios strongly increased along successional stages, however, plant N:P ratios were neither related to soil N:P stoichiometry nor to changes in soil N and P availability. Instead changes in plant nutrient stoichiometry were “driven” by plant-functional-group identity. Not only N:P ratios differed between legumes, grasses and forbs but each of these plant functional groups maintained N:P ratios relatively constant across pioneer, middle and advanced successional stages. Our evidence is that soil nutrient stoichiometry may not be a good predictor of changes in plant N:P stoichiometry along natural primary ecological successions, which have not reached yet a retrogressive stage. This could be because wild-plants rely on mechanisms of internal nutrient regulation, which make them less dependent to changes in soil nutrient availability under unpredictable environmental conditions. Further studies need to clarify what underlying evolutionary and eco-physiological mechanisms determine changes in nutrient stoichiometry in plant species distributed across natural environmental gradients.

陕西省3种主要树种叶片、凋落物和土壤N、P化学计量特征

PDF HTML阅读 XML下载 导出引用 引用提醒 陕西省3种主要树种叶片、凋落物和土壤N、P化学计量特征 DOI: 10.5846/stxb201507171508 作者: 作者单位: 西北农林科技大学林学院,西北农林科技大学黄土高原土壤侵蚀与旱地农业国家重点实验室,西北农林科技大学黄土高原土壤侵蚀与旱地农业国家重点实验室,西北农林科技大学林学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（41201088，41371506）；中国科学院西部之光资助项目（K301021304）；中国科学院陕西省森林固碳现状、速率和潜力研究（XDA05050203-05） N and P stoichiometric characteristics of leaves, litter, and soil for three dominant tree species in the Shaanxi Province Author: Affiliation: College of Forestry,Northwest ADdDdF University,Yangling,Shaanxi,Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources,Yangling,Shaanxi,Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources,Yangling,Shaanxi, 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:以陕西省29个县（市）39个样点的刺槐、辽东栎和油松林为研究对象，分析比较不同树种乔木叶片、凋落物与土壤N、P化学计量特征及其与经纬度、海拔、年均温度和年降水等环境因子间关系的异同以及三者之间可能存在的关系，以期为认识陕西省主要森林树种养分限制状况、制定合理的植被管理和恢复措施提供理论依据。结果表明：3树种叶片N、P含量及比值均为刺槐 > 辽东栎 > 油松，与叶片相比，凋落物中N、P含量变化幅度较小，为刺槐 > 辽东栎 > 油松，N：P比值为油松 > 辽东栎 > 刺槐。10-20 cm与0-10 cm土层相比，3树种中除辽东栎中P含量差异不显著外，其它指标N、P含量及N：P比值均显著下降（P < 0.05）。刺槐、辽东栎和油松叶片N、P含量与土壤N、P含量均没有显著相关性，以刺槐、辽东栎和油松3种植物叶片为总体来说，P含量与土壤P含量显著正相关（P < 0.05）。叶片N、P含量均大致表现出随着年均温度和年降水的增加而增加，随着经纬度的增加而降低的趋势，这一点在刺槐叶中最为明显。凋落物N含量随着年均温度和年降水的增加而增加，随着纬度和经度的增加而降低；P含量随着年降水和经度的增加而降低；N：P比值随着年均温度和年降水的增加而增加，随着纬度的增加而降低。研究区内，土壤N、P含量随着纬度、海拔的增加和年均温度、年降水、经度的降低而增加，N：P比值则呈相反的趋势。3树种土壤N、P含量及N：P比值中，P含量比N含量受环境影响更大，且0-10 cm和10-20 cm土层N、P含量及N：P比值与各环境因子的关系基本一致。 Abstract:Plant nutrient stoichiometry can be used to distinguish the biological entities based on element composition and responses to environmental factors. We determined the N and P stoichiometry for leaves, litter, and soil associated with 3 dominant tree species:Robinia pseucdoacacia, Quercus liaotungensis, and Pinus tabulaeformis, at 39 sites in 29 county-level cites of the Shaanxi Province. We aimed to distinguish the differences in leaf, litter, and soil N and P stoichiometry among the different tree species, and their relationships with environmental factors in the Shaanxi Province. Leaf N and P concentrations and their ratios, were Robinia pseucdoacacia > Quercus liaotungensis > Pinus tabulaeformis. Compared with plant leaves, the range and quantity of litter N and P concentration significantly reduced (P < 0.05), and the order was still Robinia pseucdoacacia > Quercus liaotungensis > Pinus tabulaeformis, while the order for the N:P ratio was Pinus tabulaeformis > Quercus liaotungensis > Robinia pseucdoacacia. There were no significant correlations (P < 0.05) between Robinia pseucdoacacia, Quercus liaotungensis, and Pinus tabulaeformis leaf N (or P) and soil N (or P), indicating that their growth was not limited by N or P. In total, there were significant correlations between leaf P and soil P (P < 0.05), which indicated that the growth of the plant was limited by P in the Shaanxi Province. Leaf N and P increased with mean annual temperature and precipitation, especially for Robinia pseucdoacacia. The leaf N:P ratio for the 3 tree species did not clearly correlate with the environmental factors. Litter N increased with mean annual temperature and precipitation, and decreased depending on the latitude and longitude. Although litter P showed no significant relationships with temperature and latitude (P < 0.05), it declined with precipitation and longitude. Litter N:P ratio increased with temperature and precipitation and decreased with latitude. Soil N and P increased with latitude and altitude, and decreased with mean annual temperature, mean annual precipitation, and longitude. The soil N:P ratios demonstrated an opposite trend. Soil P was more closely correlated with environmental factors than N, and the relationship between the 0-10 cm and 10-20 cm N and P stoichiometry in terms of environmental factors was almost the same. 参考文献 相似文献 引证文献

Can changes in soil biochemistry and plant stoichiometry explain loss of animal diversity of heathlands?

Increased atmospheric deposition rates of nitrogen (N) and sulphur (S) are known to affect soil biogeochemistry and cause a decline in plant biodiversity of heathlands. Concomitant declines of heathland invertebrates are mainly attributed to changes in vegetation composition and altered habitat structure. While there may also be effects on animals through altered plant chemistry, these have received little attention up to now. Here, we remedy this by quantifying soil nutrient and acid buffering status, vegetation composition and structure, plant nutrient stoichiometry, and densities and species richness of Diptera and Carabidae in two large heathland systems. Soil acid buffering status appeared to be a key driver for plant P availability. Sod-cutting was found to further increase plant N:P ratios, suggesting increased P-limitation. Vegetation N:P ratio was negatively linked to invertebrate density and species richness, and was found to impact fauna more strongly than vegetation structure and plant species richness. The relationship between invertebrates and plant C:N ratio was weaker and less consistent, suggesting that for invertebrates, plant P is generally more limiting than N. Our results imply that the role of plant stoichiometry is underestimated in explaining declines of heathland invertebrates, and we here provide a novel mechanistic model including this pathway. Management should therefore not only focus on restoring habitat structural complexity, attention should be paid to restoring plant stoichiometry. This can be achieved through restoring biogeochemical soil conditions, especially by mitigating soil acidification, while measures solely focusing on removal of accumulated N by means of sod-cutting should be avoided.

Consumer control as a common driver of coastal vegetation worldwide

AbstractRapid, global, anthropogenic alteration of food webs in ecosystems necessitates a better understanding of how consumers regulate natural communities. We provide a global synthesis of consumer control of vegetation in coastal wetlands, where the domineering role of physical factors such as nutrient and salinity, rather than consumers, has been emphasized for decades. Using a data set of 1748 measures of consumer effects reported in 443 experiments/observations on all continents except Antarctica, we examine the generality of consumer control in salt marshes and mangroves globally. Our analyses show that salt marsh herbivores, including insects, snails, crabs, waterfowl, small mammals, and livestock, generally and often strongly suppress plant survival, aboveground biomass, and height, while their effects on plant density, belowground biomass, reproduction, and cover are more variable. These effects occur in forbs, grasses, and shrubs, and in both seedlings and adult plants. Herbivores additionally affect plant nutrient stoichiometry, and mediate plant interactions, though their effects on plant diversity are less consistent. Higher trophic levels also affect plants, as predators facilitate plant growth through trophic cascades that suppress grazer abundance and grazing rate. In mangroves, there are also signs of consumer control, though the relatively few studies available have often focused on mangrove propagules and seedlings rather than adults. Our analyses further reveal that the strength of consumer control is regulated by many physical factors. Nutrient, disturbance, and flooding, for example, amplify the negative effects of herbivores. Along latitudinal gradients, increased temperature enhances the negative effects of ectothermic herbivores, but has no effect on those of endothermic herbivores. Consumer control of coastal plants is also apparent across study methodologies: in field and laboratory settings, in observational studies, in consumer exclusion and addition experiments, in natural and transplanted plants, and in experiments of various durations. The role of consumer control in coastal vegetation worldwide highlights the need to better recognize and theoretically conceptualize both top‐down and bottom‐up forcing and their interactions in coastal wetlands. Improved understanding and conservation of coastal wetlands will only occur if we incorporate what the science has revealed: trophic feedbacks are an important and pervasive determinant of coastal plant communities.

Plant stoichiometric responses to elevated CO2 vary with nitrogen and phosphorus inputs: Evidence from a global-scale meta-analysis.

Rising levels of atmospheric CO2 have been implicated in changes in the nitrogen (N) and phosphorus (P) content of terrestrial vegetation; however, questions remain over the role of C, N and P interactions in driving plant nutrient stoichiometry, particularly whether N and P additions alter vegetation responses to CO2 enrichment singly. Here we use meta-analysis of 46 published studies to investigate the response of plant N and P to elevated CO2 alone and in combination with nutrient (N and P) additions across temperate vs. tropical biomes. Elevated CO2 reduces plant N concentrations more than plant P concentrations in total biomass pools, resulting in a significant decline in vegetation N/P. However, elevated CO2 treatments in combination with N additions increase plant P concentrations, whereas P additions have no statistical effect on plant N concentrations under CO2 enrichment. These results point to compensatory but asymmetrical interactions between N, P and CO2; that changes in N rapidly alter the availability of P, but not the converse, in response to increased CO2. Our finding implies widespread N limitation with increasing atmospheric CO2 concentrations alone. We also suggest that increased anthropogenic N deposition inputs could enhance plant N and P in a progressively CO2-enriched biosphere.

Linking plant leaf nutrients/stoichiometry to water use efficiency on the Loess Plateau in China

Nutrient and hydrological cycles are tightly coupled in ecosystems. However, little is known about the relationship between leaf nutrient stoichiometry (nutrient mass ratios) and water use efficiency (WUE) in ecosystems. To fill this knowledge gap, we examined 132 plant samples distributed from the Qinling Mountains to the north of the Loess Plateau of China and observed the relationship between leaf nutrient stoichiometry and WUE in various ecosystems. Our findings suggest that a positive correlation exists between the leaf nitrogen:phosphorus (N:P) ratio and WUE, and this relationship is sensitive to plant life forms and growth conditions. Additionally, potassium (K) was related to WUE in herbs and plants under P limitation. These results link plant nutrient stoichiometry to hydraulic processes in terrestrial plants and provide useful information for ecologists studying nutrient and hydrological cycles in ecosystems.

Response of plant nutrient stoichiometry to fertilization varied with plant tissues in a tropical forest

Plant N:P ratios are widely used as indices of nutrient limitation in terrestrial ecosystems, but the response of these metrics in different plant tissues to altered N and P availability and their interactions remains largely unclear. We evaluated changes in N and P concentrations, N:P ratios of new leaves (<1 yr), older leaves (>1 yr), stems and mixed fine roots of seven species after 3-years of an N and P addition experiment in a tropical forest. Nitrogen addition only increased fine root N concentrations. P addition increased P concentrations among all tissues. The N × P interaction reduced leaf and stem P concentrations, suggesting a negative effect of N addition on P concentrations under P addition. The reliability of using nutrient ratios as indices of soil nutrient availability varied with tissues: the stoichiometric metrics of stems and older leaves were more responsive indicators of changed soil nutrient availability than those of new leaves and fine roots. However, leaf N:P ratios can be a useful indicator of inter-specific variation in plant response to nutrients availability. This study suggests that older leaf is a better choice than other tissues in the assessment of soil nutrient status and predicting plant response to altered nutrients using nutrients ratios.

Fire alters ecosystem carbon and nutrients but not plant nutrient stoichiometry or composition in tropical savanna.

Fire and nutrients interact to influence the global distribution and dynamics of the savanna biome, but the results of these interactions are both complex and poorly known. A critical but unresolved question is whether short-term losses of carbon and nutrients caused by fire can trigger long-term and potentially compensatory responses in the nutrient stoichiometry of plants, or in the abundance of dinitrogen-fixing trees. There is disagreement in the literature about the potential role of fire on savanna nutrients, and, in turn, on plant stoichiometry and composition. A major limitation has been the lack of fire manipulations over time scales sufficiently long for these interactions to emerge. We use a 58-year, replicated, large-scale, fire manipulation experiment in Kruger National Park (South Africa) in savanna to quantify the effect of fire on (1) distributions of carbon, nitrogen, and phosphorus at the ecosystem scale; (2) carbon: nitrogen: phosphorus stoichiometry of above- and belowground tissues of plant species; and (3) abundance of plant functional groups including nitrogen fixers. Our results show dramatic effects of fire on the relative distribution of nutrients in soils, but that individual plant stoichiometry and plant community composition remained unexpectedly resilient. Moreover, measures of nutrients and carbon stable isotopes allowed us to discount the role of tree cover change in favor of the turnover of herbaceous biomass as the primary mechanism that mediates a transition from low to high 'soil carbon and nutrients in the absence of fire. We conclude that, in contrast to extra-tropical grasslands or closed-canopy forests, vegetation in the savanna biome may be uniquely adapted to nutrient losses caused by recurring fire.