Impact of altitudinal gradients on energetics and efficiencies of N₂‐fixation in alder–cardamom agroforestry systems of the eastern Himalayas

Abstract

The impact of altitudinal gradients on the performance of alder-cardamom agroforestry systems was analyzed on nitrogenase activity, N 2 -fixation efficiency, and stand energetics and efficiencies in the eastern Himalayas. Acetylene reduction (AR activity) measurements showed that nitrogenase activity considerably increased with advancing altitudes from 500 to 800 m to a peak at 900-1,200 m. AR activity was fairly high, between 1,300 and 1,700 m, and sharply decreased in the stands between 1,800 and 2,100 m. AR activity increased in the growing season and peaked in the rainy season. This significantly coincided with cardamom flowering during the onset of growing season to full fruiting stage at peak activity period. AR activity was dependent on soil temperature and moisture and showed a positive relationship. Nodule moisture was also a limiting factor for AR activity and showed a positive correlation. Diurnal changes showed a marked variation with highest AR activity between 8 and 12 h. The performance of commercial cardamom crop is dependent on the associated shade trees. Yield potential significantly coincided with the rate of N 2 -fixation both at age chronosequence and altitudinal gradients. The management comprises growing large number of alder until 10 years and thinning, and gap filling of cardamom up to 20 years. Such maintenance caused non-equilibrium conditions that favored systems efficiency and excellent production until 20 years. System efficiency sharply declined at low rates of N 2 -fixation, AR activity, root nodule production, and agronomic yield due to the influence of stand age and altitudinal gradients. Agroforestry stands at 900-1,700 m were more energy cost-effective due to the lower energy required for perkg N-fixation with high N supply (115-155 kg ha À1 ) confirming functionally efficient than those stands at extreme higher and lower altitudinal ranges. Therefore, replantation of alder and cardamom and phase wise agroforestry rotation after 20 years could be an ecologically and economically sustainable management practice.

Pollination biology of large cardamom (Amomum subulatum Roxb.) with special emphasis on honey bees (Apis spp.) and bumble bees (Bombus spp.) pollinators

“…Large cardamom generally produces low volume per plant, but the trade-off is that it requires relatively low labour inputs. Himalayan alder (Alnus nepalensis) is a naturally occurring tree associate with cardamom, valued for its ability to provide appropriate shade, fix atmospheric N 2 , and generate nutrient rich litter which helps facilitate a more efficient cycling of nutrients (Sharma et al 2008(Sharma et al , 2010. Scientific understanding following adequate analysis of large cardamom agroforestry systems have proven this traditional practice as economically remunerative, ecologically adapted, with comparatively high carbon sequestration potential while pollination biology is yet to be fully understood (Sharma et al 2016a, b, c).…”

Sustainability of Cardamom Comparative Advantage In Central Java Province, Indonesia

“…Rational management entails replanting around the 15th year to regenerate the plantation [25]. Therefore, replantation of cardamom and phase wise agroforestry rotation after 20 years could be an ecologically and economically sustainable management practice [26].…”

Responses of symbiotic N2 fixation in Alnus species to the projected elevated CO2 environment

“…Seasonal variations in N 2 fixation activities and rates in Alnus stands N 2 fixation begins shortly after leaf emergence in spring, remains high but variable in summer, decreases in late autumn, and ceases when all the leaves have been shed (Huss-Danell 1990;Tsutsumi et al 1993;Sharma et al 2010;Tobita et al 2013a). Fluctuations in environmental conditions such as light, soil temperature, water, mineral nutrition, and pH as well as the presence of Frankia strains also affect nodule N 2 fixation activity (Pawlowski and Newton 2008;Gtari et al 2013;Tobita et al 2013b).…”