Shuli Wang

In seasonal agricultural frozen soil areas, the straw return may influence the freeze–thaw characteristics by changing the soil organic matter and porosity. Monitoring moisture and heat in the freeze–thaw period is significant for preventing spring waterlogging and reasonable planting arrangements. However, the effect of long-term straw return on the soil freeze–thaw process is still unclear. In this study, we investigated the dynamics of soil temperature (ST) and soil moisture (SM) between straw-return cropland (SF) for 29 consecutive years and no-fertilization cropland (NF) during freeze–thaw progress in northeast China. The soil in both sites underwent unidirectional freezing and bidirectional thawing processes. The soil freezing and thawing dates in the NF of the profile occurred earlier than that in the SF. The NF had higher frozen depth and freezing rate than the SF and exhibited a larger range of ST variation and higher heat transmission efficiency. The SM showed a declining trend before the ST started to decrease to a freezing point at different depths in both sites. The migrated SM in most soil layers decreased during monitoring. The relationship between SM and negative ST was a power function at different frozen depths. The SM decreased rapidly in the range of −2–0 °C in both sites. During phase changes, the SF and NF consumed 33.0 and 43.6 MJ m⁻², respectively. The results can partially explain the response of straw return to soil hydrothermal variation during the freeze-thaw process. This study may provide an integral theory for effectively utilizing agricultural soil hydrothermal resource in northeast China.

Land degradation severely affects soil functions, thereby weakening crop productivity. However, the quantitative effects of the soil organic matter (SOM) composition and soil microbial properties on maize yield remain unclear under different levels of land degradation. Here, a gradient of land degradation was selected for sampling in the Horqin Sandy Land in northeast China. The results show that the relative abundances of aliphatic and aromatic groups decreased by 21.51% and 86.01% with increasing land degradation, respectively, and the considerable increase in polysaccharide groups led to a decrease in stability and resistance to SOM decomposition. Microbial properties, such as microbial biomass carbon, basic respiration, qCO₂, and enzyme activities, decreased as a result of land degradation. The phospholipid fatty acid content and the ratio between bacteria and fungi markedly decreased with an increasing level of land degradation, and the ratio of G⁺ to G⁻ markedly increased. Correlation analysis confirmed that the microbial properties were significantly related to the SOM composition, and the random forest model indicated that fungi were key factors affecting maize yield (7.15%, p < 0.05). Moreover, the results of the structure equation modelling revealed that land degradation reduced the soil physiochemical properties, resulting in a decrease in microorganisms, causing variations in the SOM composition and directly leading to a decrease in crop yield. The effect of microorganisms (β = 0.84 ***) on maize yield was greater than that of the SOM composition (β = 0.53 **). Our investigation can provide a theoretical basis for the conservation of the cropland in Horqin Sandy Land.

Research on how plant ecological strategies (competitive, stress‐tolerant, or ruderal) vary within species may improve our understanding of plant and community responses to climate warming and also successional changes. With increasing temperature, the importance of ruderal (R) and stress tolerance (S) components is hypothesized to decrease, while the strength of the competitive (C) component should increase. Offshoots and younger plants are predicted to have greater R and smaller S components. Leaf area, leaf dry matter content, and specific leaf area were measured for 1,344 forest plants belonging to 134 species in Liangshui and Fenglin Nature Reserves in Northeastern China, and C, R, and S scores calculated for each. Linear mixed effect models were used to assess how these indicators differed among study sites (n = 2), regeneration types, ontogenetic stages, and plant life forms. The two study sites have an average annual temperature difference of 0.675°C, simulating a temperature increase of 0.630°C due to climate warming. Higher temperatures reduce low‐temperature stress and frost damage, which may explain the observed decrease in R and S scores; at the same time, plant competitive ability increased, as manifested by higher C scores. This effect was most pronounced for herbaceous plants, but nearly negligible as compared to the effect of regeneration type for trees and of ontogeny for woody species. Resprouting trees and younger woody plants had higher R scores and lower S scores, a sign of adaptation to high disturbance. In this study, a small increase in mean annual temperature led to shifts in CSR strategy components for herbaceous species, without altering the vegetation type or community composition. Offshoots and younger plants had higher R and lower S scores, shedding light on similar changes in the ecological strategies of tree communities during secondary succession, such as the transition of Quercus mongolica coppices to forest and age‐related changes in Populus davidiana–Betula platyphylla forests.