In semi-arid areas, alfalfa (Medicago sativa L.) is widely grown, but its growth is often restricted due to limited rainfall and soil nutrients, particularly phosphorus (P). Nutrient resorption is an effective strategy for dealing with nutrient shortages. Alleviation of these limited resources using film mulch and P fertilization—which are common practices in semi-arid areas—can affect the internal recycling of such nutrients. Little is known about such effects in alfalfa and the relationship between resorption efficiency and forage yield. We conducted a two-year field experiment in the semi-arid Loess Plateau of China using film mulch and P fertilization to investigate the response to long-term increasing soil water and P availability on leaf nitrogen (N), P, and potassium (K) concentrations and nutrient resorption characteristics in alfalfa. In green leaves, mulching significantly increased P concentration by an average of 5.5% but it had no significant effect on N concentration over two years, and it decreased K concentration by 16.1% in 2017. P fertilization significantly increased N concentrations to a greater degree in 2018 (8.1%) than 2017 (1.6%). P fertilization also significantly increased P concentrations by an average of 34.1% over two years. In contrast, P fertilization significantly decreased K concentration in the mulched treatment by an average of 17.3% in 2017 and 21.8% in 2018, but it had no effect in the no-mulch treatment. In senescent leaves, mulching significantly increased N concentration by an average of 3.9% and P concentration by an average of 16.7%, but it had no significant effect on K concentration over two years, while P fertilization significantly decreased N and K concentrations over two years by an average of 7.5%, and 32.8%, respectively. P fertilization significantly increased senesced P concentration by an average of 11.9% in 2017 and 17.5% in 2018; and year × mulching × P fertilization had a significant interaction on senesced leaf P concentration. For resorption efficiency, mulching decreased P resorption efficiency by an average of 3.0%, but it had no impact on N or K resorption efficiency, while P fertilization increased the N, P, and K resorption efficiencies in alfalfa by an average of 6.8%, 6.2%, and 76.4% over two years, respectively. Interactive effects of mulching and P fertilization were found on P and K resorption efficiencies over time. In addition, N and K resorption efficiencies were significantly higher in 2018 than in 2017. The application of P fertilizer without mulching resulted in positive correlations between forage yield and N, P, and K resorption efficiencies, but no correlations were observed under film mulch. That is, mulching changed the relationship between forage yield and N, P, and K resorption efficiencies in alfalfa, suggesting that N, P, and K resorption efficiencies may not be related to high yield. Our results provide new insights into the role of nutrient resorption in alfalfa in response to increasing soil water and P availability and the relationship between resorption efficiency and forage yield, which will help us to improve alfalfa yield in semi-arid regions.

Forest soil organic carbon (SOC) accumulation is regulated by plant-derived carbon inputs and soil environmental conditions, but the relative roles of litter composition and soil physicochemical properties in regulating SOC fractions remain unclear in high-elevation forest ecosystems. This study aimed to determine whether variation in SOC among different forest types was mainly associated with particulate organic carbon (POC) or mineral-associated organic carbon (MAOC), and to identify the relative roles of litter characteristics, soil physicochemical properties, microbial biomass, and enzyme activities in regulating SOC fractions. Four forest types on the eastern edge of the Tibetan Plateau were investigated: broadleaved poplar forest (PLF), larch forest (LXF), seabuckthorn forest (SBF), and Dasiphora shrubland (DS). PLF had the highest SOC and POC contents (75.8 and 48.5 g kg⁻¹, respectively), whereas MAOC did not differ significantly among forest types. SOC was strongly positively correlated with POC (R² = 0.74, p < 0.001), but not with MAOC, indicating that SOC variation was mainly associated with POC accumulation. PLF litter contained higher labile and recalcitrant carbon components, including soluble sugar (19.9 g kg⁻¹), starch (30.1 g kg⁻¹), lignin (94.6 g kg⁻¹), and litter carbon (404 g kg⁻¹). Partial least squares path modeling showed that soil physicochemical properties had the strongest direct path relationship with SOC variation (p < 0.001), while litter composition was positively associated with microbial biomass and POC formation (p < 0.01). These findings suggest that POC formation was the main fraction-level feature associated with SOC accumulation, while soil properties and litter composition were related to SOC through different pathways.

Rational agronomic practice enhances crop productivity and resource use efficiency. Plastic film mulching and phosphorus (P) fertilization are widely applied in alpine agriculture to improve soil water content, temperature, and P availability. However, their effects on soil P transformation and nutrient uptake in faba bean (Vicia faba L.) remain unclear. This study conducted a field experiment to explore the effects of mulching methods and P levels on soil P fractions and nitrogen (N), P uptake in faba bean. The experiment followed a randomized block design with three film mulching treatments—no-mulching with flat planting (NMF), double ridges and furrows mulched with one film (DRM), and three ridges and furrows mulched with one film (TRM) and three P levels—P0 (0 kg P ha⁻¹), P1 (9.10 kg P ha⁻¹), and P2 (18.2 kg P ha⁻¹). The results showed that soil medium- and highly active P increased, while low-active P decreased with increasing P levels. Compared with DRM and TRM, NMF had lower low-active P and higher medium- and highly active P, particularly under P2. These changes contributed to increases in soil total P and available P. The aboveground N, P uptake and N/P ratio under NMF were significantly higher than under DRM and TRM. As P levels increased, the aboveground N, P uptake and N/P ratio increased in NMF and DRM, but decreased in TRM. In all treatments, the aboveground N/P ratio was below 14, indicating N limitation. NMF, especially with P2, alleviated N limitation to faba bean growth. Overall, NMF combined with about 18.2 kg P ha⁻¹ P fertilizer is a sustainable practice for faba bean cultivation in alpine regions. However, attention should be paid to achieving a balanced supply of N and P fertilizers.