Publications

Abandonment of croplands ongoing on 220 million ha worldwide contributes strongly to soil restoration by improvement of degraded properties and medium- and long-term carbon (C) sequestration in post-agricultural ecosystems. Two interrelated processes – decomposition and stabilization of soil organic carbon (SOC) – govern SOC dynamics and affect the C source or sink functions of former croplands. We investigated how the abandonment of arable soils affects (i) accumulation of SOC, its composition, stability, and turnover during the post-agricultural restoration of soils, and (ii) microbial activity parameters. A chronosequence study was carried in two bioclimatic zones of European Russia: deciduous forest (Luvic Phaeozems, PH-chronosequence) and dry steppe (Calcic Chernozems, CH-chronosequence). Each chronosequence included an arable soil, 3–4 soils abandoned at increasing time periods (up to 35 years), and natural soil: never cropped Phaeozem and completely restored Chernozem. We combined the results of nuclear magnetic resonance (NMR), thermal analysis including Differential Scanning Calorimetry and Derivative Thermogravimetry, long-term incubation for SOC mineralization, and microbiological activity (basal respiration and microbial C content). Degraded Phaeozems with low SOC amount had much higher relative increase in SOC content (134%) during the post-agricultural restoration compared to SOC-rich Chernozems (38%). SOC gains were recorded in all organic compound classes identified by NMR and thermal analysis, but the increase of recalcitrant SOC was more pronounced in the post-agricultural Chernozems than in the Phaeozems. The post-agricultural Chernozems were characterized by higher SOC aliphaticity and aromaticity than Phaeozems. Microbial activity and biodegradable SOC increased gradually during post-agricultural restoration. Being mostly a function of climate and vegetation, the soil type was the primary factor explaining the greatest portion (54–88%) of the total variance for most soil and microbial parameters. Concluding, despite SOC content increased in both Chernozems and Phaeozems during the post-agricultural restoration, the mechanisms of C sequestration and stabilization were dependent on climate, vegetation, and on the degradation intensity during the agricultural use. The accumulation of organic compounds was specific for virgin soils dominating in deciduous forest and steppes, and had direct consequences for microbial activities, C turnover and sequestration.

Land-use intensification in the tropics plays an important role in meeting global demand for agricultural commodities but generates high environmental costs. Here, we synthesize the impacts of rainforest conversion to tree plantations of increasing management intensity on carbon stocks and dynamics. Rainforests in Sumatra converted to jungle rubber, rubber, and oil palm monocultures lost 116 Mg C ha-1, 159 Mg C ha-1, and 174 Mg C ha-1, respectively. Up to 21% of these carbon losses originated from belowground pools, where soil organic matter still decreases a decade after conversion. Oil palm cultivation leads to the highest carbon losses but it is the most efficient land use, providing the lowest ratio between ecosystem carbon storage loss or net primary production (NPP) decrease and yield. The imbalanced sharing of NPP between short-term human needs and maintenance of long-term ecosystem functions could compromise the ability of plantations to provide ecosystem services regulating climate, soil fertility, water, and nutrient cycles.

Kobresia pastures in the eastern Tibetan highlands occupy 450000 km 2 and form the world’s largest pastoral alpine ecosystem. The main constituent is an endemic dwarf sedge, Kobresia pygmaea , which forms a lawn with a durable turf cover anchored by a felty root mat, and occurs from 3000 m to nearly 6000 m a.s.l. The existence and functioning of this unique ecosystem and its turf cover have not yet been explained against a backdrop of natural and anthropogenic factors, and thus its origin, drivers, vulnerability or resilience remain largely unknown. Here we present a review on ecosystem diversity, reproduction and ecology of the key species, pasture health, cycles of carbon (C), water and nutrients, and on the paleo-environment. The methods employed include molecular analysis, grazing exclusion, measurements with micro-lysimeters and gas exchange chambers, 13 C and 15 N labelling, eddy-covariance flux measurements, remote sensing and atmospheric modelling. The following combination of traits makes Kobresia pygmaea resilient and highly competitive: dwarf habit, predominantly below-ground allocation of photo assimilates, mixed reproduction strategy with both seed production and clonal growth, and high genetic diversity. Growth of Kobresia pastures is co-limited by low rainfall during the short growing season and livestock-mediated nutrient withdrawal. Overstocking has caused pasture degradation and soil deterioration, yet the extent remains debated. In addition, we newly describe natural autocyclic processes of turf erosion initiated through polygonal cracking of the turf cover, and accelerated by soil-dwelling endemic small mammals. The major consequences of the deterioration of the vegetation cover and its turf include: (1) the release of large amounts of C and nutrients and (2) earlier diurnal formation of clouds resulting in (3) decreased surface temperatures with (4) likely consequences for atmospheric circulation on large regional and, possibly global, scales. Paleo-environmental reconstruction, in conjunction with grazing experiments, suggests that the present grazing lawns of Kobresia pygmaea are synanthropic and may have existed since the onset of pastoralism. The traditional migratory rangeland management was sustainable over millennia and possibly still offers the best strategy to conserve, and possibly increase, the C stocks in the Kobresia turf, as well as its importance for climate regulation.

No abstract is provided for this article.

Microbial interactions in soil are hidden, as they occur stealthily in a ‘dark box’. This greatly limits our understanding of microbial functions. Here, soil microorganisms were classified into three broad functional groups, namely miners, scavengers and carriers, to disentangle the intricate microbial labor division and interactions for nutrient acquisition. Miners, such as saprotrophic microorganisms, N2-fixing and phosphate-solubilizing bacteria, and ectomycorrhizal (ECM) fungi, first decompose or mobilize not directly bioavailable organic or inorganic substances through hydrolysis, oxidation and/or mineralization. Scavengers, arbuscular mycorrhizal (AM) fungi as a typical example, explore and efficiently take up nutrients with assistance of host plants, but cannot access nutrients stored in organic matter or minerals. Carriers with filamentous growth such as ECM, AM and saprotrophic fungi transport nutrients and unicellular bacteria to new locations exploiting a large soil volume for nutrients. These three groups build ‘division of labor’ and interaction networks, which reduce the metabolic burden, increase substrate utilization efficiency, and ultimately increase nutrient acquisition in the rhizosphere, detritusphere, and bulk soil. Notably, such grouping of soil microorganisms based on functions is flexible, and a particular microorganism can be versatile. Flexibility in ecological functions and consequence of interactions is necessary to respond to shifting soil nutrient content, organic matter availability, and edaphic conditions. Nevertheless, such broad grouping is conducive to condense functional diversity and allows a better understanding of mutualistic interactions among microbial groups, contributing to hotspot formation and disappearance, nutrient mobilization and delivery to roots. A combination of laboratory studies on pairwise interactions, experiments using synthetic microbial communities with network analysis and imaging techniques is essential to unravel tangled webs of microbial associations. In summary, the interactions among microbial groups classified based on their interconnected ecological processes as miners, scavengers and carriers are important to uncover the true functional roles of microorganisms in terrestrial ecosystems.

The author regret that a typographical error was present in the Fig. 2 of the published original version of this article; the text “Natual&#

Topsoil carbon (C) stocks are known to decrease as a consequence of the conversion of natural ecosystems to plantations or croplands; however, the effect of land use change on subsoil C remains unknown. Here, we hypothesized that the effect of land use change on labile subsoil organic C may be even stronger than for topsoil due to upward concentration of plantations and crops root systems. We evaluated soil labile organic C fractions, including particulate organic carbon (POC) and its components [coarse POC and fine POC], light fraction organic carbon (LFOC), readily oxidizable organic carbon, dissolved organic carbon (DOC) and microbial biomass down to 100 cm soil depth from four typical land use systems in subtropical China. Decrease in fine root biomass was more pronounced below 20 cm than in the overlying topsoil (70% vs. 56% for plantation and 62% vs. 37% for orchard. respectively) driving a reduction in subsoil labile organic C stocks. Land use changes from natural forest to Chinese fir plantation, Chinese chestnut orchard, or sloping tillage reduced soil organic C stocks and that of its labile fractions both in top and subsoil (20–100 cm). POC reduction was mainly driven by a decrease in fine POC in topsoil, while DOC was mainly reduced in subsoil. Fine POC, LFOC and microbial biomass can be useful early indicators of changes in topsoil organic C. In contrast, LFOC and DOC are useful indicators for subsoil. Reduced proportions of fine POC, LFOC, DOC and microbial biomass to soil organic C reflected the decline in soil organic C quality caused by land use changes. We conclude that land use changes decrease C sequestration both in topsoil and subsoil, which is initially indicated by the labile soil organic C fractions.

Unprecedented nitrogen (N) inputs into terrestrial ecosystems have profoundly altered soil N cycling. Ammonia oxidizers and denitrifiers are the main producers of nitrous oxide (N2 O), but it remains unclear how ammonia oxidizer and denitrifier abundances will respond to N loading and whether their responses can predict N-induced changes in soil N2 O emission. By synthesizing 101 field studies worldwide, we showed that N loading significantly increased ammonia oxidizer abundance by 107% and denitrifier abundance by 45%. The increases in both ammonia oxidizer and denitrifier abundances were primarily explained by N loading form, and more specifically, organic N loading had stronger effects on their abundances than mineral N loading. Nitrogen loading increased soil N2 O emission by 261%, whereas there was no clear relationship between changes in soil N2 O emission and shifts in ammonia oxidizer and denitrifier abundances. Our field-based results challenge the laboratory-based hypothesis that increased ammonia oxidizer and denitrifier abundances by N loading would directly cause higher soil N2 O emission. Instead, key abiotic factors (mean annual precipitation, soil pH, soil C:N ratio, and ecosystem type) explained N-induced changes in soil N2 O emission. Altogether, these findings highlight the need for considering the roles of key abiotic factors in regulating soil N transformations under N loading to better understand the microbially mediated soil N2 O emission.

Systematic assessment of arable land use is a fundamental prerequisite to explore its sustainable development path. Agricultural infrastructure integrated with the tillage conditions and soil properties was used to evaluate the state of regional arable land use and its potential for sustainable productivity. We propose a combined weighting method integrating Delphi and entropy weights to consider both decision objectives and indicator attributes. The proposed approach takes into account both expertise and data feature, making the evaluating results more rational and applicable. The impacts of large‐scale land use change and regional urban distribution on soil properties and agricultural infrastructure were also explored to develop more rational and differentiated conservation strategies. Our evaluation showed that 44% and 48% of the soil properties of arable land in Heilongjiang Province, China, are in the excellent or good grades, respectively, meaning that no or only minor remediation measures are needed to achieve optimum conditions. Agricultural infrastructure deserves more attention from the management than soil properties, as only 16% and 24% of area have the same excellent and good grades. The results of the evaluation with a combination of subjective and objective weights are closer to a normal distribution curve than if only expert weights are used, which confirms our hypothesis that the new weighting method is more reasonable. The newly proposed weighted design method and index provide a better understanding of the sustainable productivity of agricultural areas and have a promising application in large‐scale black soil areas worldwide. The future rough growth strategy for resources will result in degradation and posed risks to regional ecological conservation. At the provincial level (up to 130 km), agricultural infrastructure declines and then rises as fields move away from cities, with the inflection point at 55 km. State‐owned farms are mainly responsible for this inflection point, which shift the agents of arable land from small farmers to large capital, with remote arable land receiving more investment. The impact mechanisms of urbanization should be deeper explored to address the challenges for arable land conservation.