Bioavailable soil phosphorus decreases with increasing elevation in a subarctic tundra landscape

Spatial variation of sulfur in terrestrial ecosystems in China: Content, density, and storage

Sulfur (S) is an important macronutrient that is widely distributed in nature. Understanding the patterns and mechanisms of S dynamics is of great significance for accurately predicting the geophysical and chemical cycles of S and formulating policies for S emission and management. We systematically investigated and integrated 17,618 natural plots in China's terrestrial ecosystems and built a S density database of vegetation (including leaves, branches, stems, and roots) and surface soil (0-30 cm depth). The biogeographic patterns and environmental drivers of the S content, density, and storage in the vegetation and soil of terrestrial ecosystems were explored. Vegetation and soil were the major components of terrestrial ecosystems, storing a total of 2228.77 ± 121.72 Tg S, with mean S densities of 4.32 ± 0.04 × 10-2, and 267.93 ± 14.94 × 10-2 t hm-2, respectively. The forest was the most important vegetation S pool and their S storage accounted for about 55.28 % of the total vegetation S storage, whereas soil S pools of croplands and other vegetation types (e.g., deserts and wetlands) accounted for about 63.18 % of the total soil S storage. The mean S density (2.18 ± 0.02 × 10-2 t hm-2) and S storage (12.45 ± 0.31 Tg) of plant roots were significantly higher than those of other organs. The spatial variation in the S density was mainly regulated by climate and soil properties, reflecting the physiological adaptation mechanisms of plants by adjusting the S uptake and distribution to cope with climate change. In this study, the spatial patterns of S density and storage in vegetation and soil in terrestrial ecosystems of China and their response to environmental factors on a national scale were systematically studied. The results provide insights into the biological functions of S and its role in plant-environment interactions.

Driving factors of community-level leaf stoichiometry patterns in a typical temperate mountain meadow ecosystem of northern China

In ecological stoichiometry, the stoichiometry and spatial distribution of leaf carbon, nitrogen, and phosphorus are important research topics. Various studies have assessed leaf stoichiometry and its relationships with environmental factors at different scales. However, how the leaf carbon, nitrogen and phosphorus stoichiometric characteristics of the same vegetation type at the community level vary with environmental factors along a continuous altitudinal gradient remains poorly understood. In this paper, 13 sampling sites along an altitudinal gradient of 1,800-3,011 m in a typical temperate mountain meadow ecosystem on the southern slope of the Wutai Mountain in North China were sampled to explore the response of leaf carbon, nitrogen and phosphorus stoichiometric characteristics to altitude change using correlation analysis, and then quantified the contribution of driving factors using canonical correspondence analysis (CCA) and variation partitioning. We found that the community-level leaf stoichiometry of mountain meadows differed significantly at different altitudes, and an increase in altitude significantly decreased community-level leaf total nitrogen (LTN) and leaf total phosphorus (LTP); however, the leaf total carbon (LTC), C∶N, C∶P, and N∶P increased with an increase in altitude. Additionally, with increasing altitude, soil properties showed significant trends. Soil organic carbon (SOC), soil total nitrogen (STN), soil total phosphorus (STP), soil water content and soil electrical conductivity increased significantly, but soil temperature, soil bulk density and soil pH exhibited the opposite trend. Our results suggested that altitude, soil electrical conductivity and soil bulk density significantly influenced the changes in the leaf stoichiometric characteristics, explaining 75.5% of the total variation, and altitude had the greatest influence (36.6%). In the temperate mountains, altitude played a decisive role in affecting patterns of meadow plant nutrients and stoichiometry and was more important than soil in explaining leaf C∶N∶P stoichiometry variations. Our findings provide important references to understand the responses of plant stoichiometry to altitudinal gradients.

Response of spatio-temporal changes in sediment phosphorus fractions to vegetation restoration in the degraded river-lake ecotone

Phosphorus (P) is an essential element in the ecosystem and the cause of the eutrophication of rivers and lakes. The river-lake ecotone is the ecological buffer zone between rivers and lakes, which can transfer energy and material between terrestrial and aquatic ecosystems. Vegetation restoration of degraded river-lake ecotone can improve the interception capacity of P pollution. However, the effects of different vegetation restoration types on sediment P cycling and its mechanism remain unclear. Therefore, we seasonally measured the P fractions and physicochemical properties of sediments from different restored vegetation (three native species and one invasive species). The results found that vegetation restoration significantly increased the sediment total P and bioavailable P content, which increased the sediment tolerance to P pollution in river-lake ecotone. In addition, the total P content in sediments was highest in summer and autumn, but lower in spring and winter. The total P and bioavailable P contents in surface sediments were the highest. They decreased with increasing depth, suggesting that sediment P assimilation by vegetation restoration and the resulting litter leads to redistribution of P in different seasons and sediment depths. Microbial biomass-P (MBP), total nitrogen (TN), and sediment organic matter (SOM) are the main factors affecting the change of sediment phosphorus fractions. All four plants' maximum biomass and P storage appeared in the autumn. Although the biomass and P storage of the invasive species Alternanthera philoxeroides were lower, the higher bioavailable P content and MBP values of the surface sediments indicated the utilization efficiency of sediment resources. These results suggest that vegetation restoration affects the distribution and circulation of P in river and lake ecosystems, which further enhances the ecological function of the river-lake ecotone and prevents the eutrophication and erosion of water and sediment in the river-lake ecotone.

Temperature and soils predict the distribution of plant species along the Himalayan elevational gradient

Tropical montane systems are characterized by a high plant species diversity and complex environmental gradients. Climate warming may force species to track suitable climatic conditions and shift their distribution upward, which may be particularly problematic for species with narrow elevational ranges. To better understand the fate of montane plant species in the face of climate change, we evaluated a) which environmental factors best predict the distribution of 277 plant species along the Himalayan elevational gradient in Nepal, and b) whether species elevational ranges increase with increasing elevation. To this end, we developed ecological niche models using MaxEnt by combining species survey and presence data with 19 environmental predictors. Key environmental factors that best predicted the distribution of Himalayan plant species were mean annual temperature (for 54.5% of the species) followed by soil clay content (10.2%) and slope (9.4%). Although temperature is the best predictor, it is associated with many other covariates that may explain species distribution, such as irradiance and potential evapotranspiration. Species at both ends of the Himalayan elevational gradient had narrower elevational ranges than species in the middle. Our results suggest that with further global warming, most Himalayan plant species have to migrate upward, which is especially critical for upland species with narrow distribution ranges.

Decomposition rate and stabilization across six tundra vegetation types exposed to >20 years of warming

AIMS

Litter decomposition is an important driver of soil carbon and nutrient cycling in nutrient-limited Arctic ecosystems. However, climate change is expected to induce changes that directly or indirectly affect decomposition. We examined the direct effects of long-term warming relative to differences in soil abiotic properties associated with vegetation type on litter decomposition across six subarctic vegetation types.

METHODS

In six vegetation types, rooibos and green tea bags were buried for 70-75 days at 8 cm depth inside warmed (by open-top chambers) and control plots that had been in place for 20-25 years. Standardized initial decomposition rate and stabilization of the labile material fraction of tea (into less decomposable material) were calculated from tea mass losses. Soil moisture and temperature were measured bi-weekly during summer and plant-available nutrients were measured with resin probes.

RESULTS

Initial decomposition rate was decreased by the warming treatment. Stabilization was less affected by warming and determined by vegetation type and soil moisture. Soil metal concentrations impeded both initial decomposition rate and stabilization.

CONCLUSIONS

While a warmer Arctic climate will likely have direct effects on initial litter decomposition rates in tundra, stabilization of organic matter was more affected by vegetation type and soil parameters and less prone to be affected by direct effects of warming.

Altitude and Vegetation Affect Soil Organic Carbon, Basal Respiration and Microbial Biomass in Apennine Forest Soils

Both altitude and vegetation are known to affect the amount and quality of soil organic matter (SOM) and the size and activity of soil microbial biomass. However, when altitude and vegetation changes are combined, it is still unclear which one has a greater effect on soil chemical and biochemical properties. With the aim of clarifying this, we tested the effect of altitude (and hence temperature) and vegetation (broadleaf vs pine forests) on soil organic carbon (SOC) and soil microbial biomass and its activity. Soil sampling was carried out in two adjacent toposequences ranging from 500 to 1000 m a.s.l. on a calcareous massif in central Italy: one covered only by Pinus nigra J.F. Arnold forests, while the other covered by Quercus pubescens Willd., Ostrya carpinifolia Scop. and Fagus sylvatica L. forests, at 500, 700 and 1000 m a.s.l., respectively. The content of SOC and water-extractable organic carbon (WEOC) increased with altitude for the pine forests, while for the broadleaf forests no trend along the slope occurred, and the highest SOC and WEOC contents were observed in the soil at 700 m under the Ostrya carpinifolia forest. With regard to the soil microbial community, although the size of the soil microbial biomass (Cmic) generally followed the SOC contents along the slope, both broadleaf and pine forest soils showed similar diminishing trends with altitude of soil respiration (ΣCO2-C), and ΣCO2-C:WEOC and ΣCO2-C:Cmic ratios. The results pointed out that, although under the pine forests’ altitude was effective in affecting WEOC and SOC contents, in the soils along the broadleaf forest toposequence this effect was absent, indicating a greater impact of vegetation than temperature on SOC amount and pool distribution. Conversely, the similar trend with altitude of the microbial activity indexes would indicate temperature to be crucial for the activity of the soil microbial community.

Climatic and topographic variables control soil nitrogen, phosphorus, and nitrogen: Phosphorus ratios in a Picea schrenkiana forest of the Tianshan Mountains

Knowledge about soil nitrogen (N) and phosphorus (P) concentrations, stocks, and stoichiometric ratios is crucial for understanding the biogeochemical cycles and ecosystem function in arid mountainous forests. However, the corresponding information is scarce, particularly in arid mountainous forests. To fill this gap, we investigated the depth and elevational patterns of the soil N and P concentrations and the N: P ratios in a Picea schrenkiana forest using data from soil profiles collected during 2012-2017. Our results showed that the soil N and P concentrations and the N: P ratios varied from 0.15 g kg-1 to 0.56 g kg-1 (average of 0.31 g kg-1), from 0.09 g kg-1 to 0.16 g kg-1 (average of 0.12 g kg-1), and from 2.42 g kg-1 to 4.36 g kg-1 (average of 3.42 g kg-1), respectively; additionally, values significantly and linearly decreased with soil depth. We did not observe a significant variation in the soil N and P concentrations and the N: P ratios with the elevational gradient. In contrast, our results revealed that the mean annual temperature and mean annual precipitation exhibited a more significant influence on the soil N and P concentrations and the N: P ratios than did elevation. This finding indicated that climatic variables might have a more direct impact on soil nutrient status than elevation. The observed relationship among the soil N and P concentrations and the N: P ratios demonstrated that the soil N was closely coupled with the soil P in the P. schrenkiana forest.

A global dataset of plant available and unavailable phosphorus in natural soils derived by Hedley method

Soil phosphorus (P) fractions are critical for understanding soil P dynamics and availability. This paper provides a global dataset of soil P fractions separated by the Hedley method. The dataset also includes key environmental factors associated with soil P dynamics and availability, including climate factors, vegetation, soil and parent material types, soil age, and soil physiochemical properties such as particle size, bulk density, pH in water, organic carbon, total nitrogen, and extractable iron and aluminium concentrations. This dataset includes measures of Hedley P fractions of 802 soil samples and was gathered through a literature survey of 99 published studies. Plant availability of each soil P fraction was noted. We anticipate that the global dataset will provide valuable information for studying soil P dynamics and availability, and it will be fused into earth system models to better predict how terrestrial ecosystems will respond to global environmental changes.

Altitudinal patterns and controls of plant and soil nutrient concentrations and stoichiometry in subtropical China

Altitude is a determining factor of ecosystem properties and processes in mountains. This study investigated the changes in the concentrations of carbon (C), nitrogen (N), and phosphorus (P) and their ratios in four key ecosystem components (forest floor litter, fine roots, soil, and soil microorganisms) along an altitudinal gradient (from 50 m to 950 m a.s.l.) in subtropical China. The results showed that soil organic C and microbial biomass C concentrations increased linearly with increasing altitude. Similar trends were observed for concentrations of total soil N and microbial biomass N. In contrast, the N concentration of litter and fine roots decreased linearly with altitude. With increasing altitude, litter, fine roots, and soil C:N ratios increased linearly, while the C:N ratio of soil microbial biomass did not change significantly. Phosphorus concentration and C:P and N:P ratios of all ecosystem components generally had nonlinear relationships with altitude. Our results indicate that the altitudinal pattern of plant and soil nutrient status differs among ecosystem components and that the relative importance of P vs. N limitation for ecosystem functions and processes shifts along altitudinal gradients.