Influence of peach (Prunus persica Batsch) phenological stage on the short-term changes in oxidizable and labile pools of soil organic carbon and activities of carbon-cycle enzymes in the North-Western Himalayas

The labile organic carbon (C) and C-related enzymes are sensitive indicators capturing alterations of soil organic matter (SOM), even in a short-time scale. Although the effects of crop husbandry and land use change on these attributes have been well studied, there is no consensus about how plant phenology may impact them. This study aimed to determine the short-term effect of six distinct phenological stages (PS-1: full bloom; PS-2: fruit set; PS-3: pit hardening; PS-4: physiological maturity; PS-5: 60 d after physiological maturity; and PS-6: fall) of peach on the changes in soil organic carbon (SOC) fractions of different oxidizability, labile C pools, and C-cycle enzyme activities in soils, for two consecutive years (2015 and 2016) in the North-Western Himalayas (NWH). Peach rhizosphere soils were sampled at the topsoil (0–15 cm) and subsoil (16–30 cm) layers, along with rhizosphere soils from adjacent perennial grasses, which served as a control. Values for most of the assessed parameters, including very labile C, labile C, microbial biomass C, permanganate oxidizable C, dissolved organic C, mineralizable C, amylase activity, and carboxymethyl-cellulase activity, were significantly (P ≤ 0.05) higher at PS-3 than at other phenological stages of peach. Conversely, a sudden decline in these soil variables was recorded at PS-5, followed by a slight buildup at PS-6, particularly in the topsoil of the peach orchard. Short-term changes in organic C fractions of different oxidizability, influenced by peach phenological stage, significantly (P ≤ 0.05) affected C management index, C pool index, and lability index. Both the C management index and lability index showed their highest values at PS-3 and their lowest values at PS-5, clearly indicating short-term accretion and depletion of SOC, in tandem with the peach phenological events. Principal component analysis suggested that a composite of soil indicators, including microbial biomass C, dissolved organic C, amylase, and invertase, could help detect short-term changes in SOC content. It is concluded that peach phenological events had a major impact on the short-term variations of the studied soil variables, which could be attributed to changes in the above- and belowground plant residues, as well as the extent of nutrients and water acquisition.