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The carbon cycle and underlying environmental drivers are not yet fully understood, and whether climate warming is inducing soil carbon loss remains controversial, largely due to limited evidence from large‐scale observations. With relatively less human disturbance, Yunnan Province, a typical mountainous plateau region in Southwest China, is a favorable place to evaluate environmental effects on soil organic carbon (SOC) dynamics. In this study, soil sampling of the upper 20‐cm soil layer was conducted at sites across Yunnan Province in 1986 and 2010 to estimate topsoil SOC density (SOCD). The changes in SOCD and environmental factors, including initial SOCD value, temperature, precipitation, longitude, latitude, elevation, and slope gradient, were analyzed. The results indicated that the topsoil of Yunnan Province mainly acted as a carbon source during the study period. The topsoil SOCD in 1986 averaged 5.82 kg C m−2 and was higher than that of 2010 (5.45 kg C m−2), corresponding to a 0.14 Pg loss in SOC stock over the 25 years. The northwestern subregion experienced the most drastic SOCD changes, and the SOCD decreased most notably in areas with higher initial SOCD values. Compared with cropland and grassland, more significant SOCD reductions were observed in forest. Among the studied environmental factors, initial SOCD was the main factor associated with SOCD variations. The next most important factor was temperature, followed by precipitation. With high elevation and initial SOCD, the northwestern subregion of Yunnan Province had the most sensitive SOCD changes, underscoring the need for further protection and appropriate management.

• Background and Aims Depending on the species, water stress affects different growth and developmental processes, mainly due to changes in hydraulic properties and hormonal signalling. This study compared the impact of water stress on tree development and organ growth in three apple cultivars. • Methods Trees were differentially irrigated to induce water stress or to provide well-watered conditions in their second and third years of growth. Effects of water stress were evaluated at tree scale by shoot number and proportions of the different types of shoots, and at shoot scale by metamer appearance rate, growth duration and arrest time, as well as organ size. • Key Results Water stress promoted early growth cessation, prolonged summer arrests and decreased growth resumptions, thus modifying within-tree shoot demography in favour of short shoots. Growth cessations occurred in mild water stress conditions before any difference in stem water potential appeared. No major impact was observed on organ size. Consistently with tree ontogeny, the number of shoots that resumed growth after summer arrest decreased with years, but more in water-stressed than well-watered conditions. • Conclusions Even though the impact of water stress differed slightly among cultivars, the reduction in neoformation and increase in summer arrest played a common role in apple tree morphological responses and led to stress avoidance by early reduction of tree leaf area.

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