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Impact of altitudinal gradients on energetics and efficiencies of N 2 ‐fixation in alder–cardamom agroforestry systems of the eastern Himalayas
Author(s) -
Sharma G.,
Sharma R.,
Sharma E.
Publication year - 2010
Publication title -
ecological research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.628
H-Index - 68
eISSN - 1440-1703
pISSN - 0912-3814
DOI - 10.1007/s11284-009-0628-z
Subject(s) - chronosequence , nitrogenase , biology , growing season , alder , nitrogen fixation , agronomy , shading , energetics , botany , horticulture , ecology , ecosystem , genetics , bacteria , art , visual arts
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 per‐kg N‐fixation with high N supply (115–155 kg ha −1 ) 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.