Effect of multipurpose tree species on soil fertility and CO2 efflux under hilly ecosystems of Northeast India

Abstract

A 26 years old agroforestry plantation consisting of four multipurpose tree species (MPTs) (Michelia oblonga Wall, Parkia roxburghii G. Don, Alnus nepalensis D. Don, and Pinus kesiya Royle ex - Gordon) maintained at ICAR Research Complex, Umiam, Meghalaya, India were compared with a control plot (without tree plantation) for soil fertility status and CO2 efflux. The presence of trees improved all the physico - chemical and microbial biomass parameters studied in this experiment. Relative to control, soils under MPTs showed significant increases of 17 % soil organic carbon, 26 % available nitrogen (AN), 28 % phosphorus (AP), 50 % potassium (AK), 65 % mean weight diameter (MWD) of aggregates, 21 % moisture and 34 % soil microbial biomass carbon (MBC) while reducing the mean bulk density (7 %). However, these parameters significantly differed among the tree species i.e., soils under A. nepalensis and M. oblonga had higher values of these attributes except bulk density, than under other species. Irrespective of treatments, the values of all these attributes were higher in surface soils while bulk density was highest in subsurface (60–75 cm). Cumulative CO2 efflux under MPTs was significantly higher (15 %) and ranged from 1.71 g 100 g - 1 (M. oblonga) to 2.01 g 100 g - 1 (A. nepalensis) compared to control at 150 days of incubation. In all the treatments, increment in temperature increased the oxidation of soil organic matter, thereby increased the cumulative CO2 efflux from soils. Of the tree species, with increment in temperature, A. nepalensis recorded more CO2 efflux (2.50 g 100 g - 1) than other MPTs but the per cent increase was more in control plot. P. kesiya and A. nepalensis recorded highest activation energy (59.1 and 39 kJ mol - 1, respectively). Net organic carbon sequestered in soil was highest under A. nepalensis (25.7 g kg - 1) followed by M. oblonga (19.3 g kg - 1), whereas control showed the lowest values. Amount of net carbon stored in the soil had significant and positive correlation with MBC (r = 0.706 * *), MWD (r = 0.636 *), and AN (r = 0.825 * *).