No abstract

The eastern Himalayan region of Northeast India is well known for its traditional home gardens, which are considered to play important roles in the maintenance of livelihoods of indigenous communities and conservation of biological diversity. This study determines the plant diversity in home gardens and their importance in conservation of plant genetic resources (PGR) through utilization. We studied 90 home gardens in detail located in six villages. Different aspects of the home gardens and plant species were observed directly and through discussion with the farmers. A total of 333 plant species (133 trees, 92 shrubs, and 108 herbs) belonging to 128 plant families with an average of 78 species per home garden were recorded. The size of home gardens ranged between 0.10 and 0.60 ha and showed significant (P<0.001) positive correlation between the garden size and plant species diversity. The species diversity index for trees, shrubs, and herbs was 4.76, 4.39, and 4.58, respectively. The species similarity within each life form was high with 50% for trees, 38% for shrubs, and 49% for herbs. Plant species in the home gardens could be grouped into 11 major use categories with the majority of plants in the medicinal or multiple use category. These home gardens are reservoirs of PGR and play a vital role in sustaining the livelihood of local inhabitants. They are also functioning as domestication and conservation centers of many crop relatives.

Rates of weight loss and nutrient (N and P) release patterns were studied in the leaf litter of the dominant tree species (Ailanthus grandis, Altingia excelsa, Castanopsis indica, Duabanga sonneriatioides, Dysoxylum binectariferum, Mesua ferrea, Shorea assamica, Taluma hodgsonii, Terminalia myriocarpa and Vatica lancefolia) of a tropical wet evergreen forest of northeast India. Nitrogen and phosphorus mineralization rate and decay pattern varied significantly from species to species. In general, the decay pattern, characterized by using a composite polynomial regression equation, exhibited three distinct phases of decay during litter decomposition-an initial slow decay phase (0.063% weight loss day -1 ), followed by a rapid decay phase (0.494% weight loss day -1 ) and a final slow decay phase (0.136% weight loss day -1 ). The initial chemical composition of the litter affected decomposition rates and patterns. Species like D. sonneriatoides, D. binectariferum, and T. hodgsonii with higher N and P content, lower carbon and lignin content, and lower C:N ratio and lignin:N ratio exhibited relatively faster decomposition rates than the other species, for example M. ferrea, C. indica and A. grandis. A slow decay rate was recorded for species such as M. ferrea, C. indica, and A. grandis. The initial N and P content of litter showed significant positive correlations with decay rates. Carbon and lignin content, lignin:N, and C:N showed significant negative correlations with decay rates. Soil total N and P, and rainfall, soil temperature, and soil moisture had positive correlations with decay rates. The rapid decomposition rates observed in comparison with other different forest litter decay rates confirm that tropical wet evergreen forest species are characterized by faster decomposition rates, indicating a faster rate of organic matter turnover and rapid nutrient cycling.

Citron (Citrus medica L.) is a medicinally important species of citrus native to India and occurs in natural forests and home gardens in the foothills of the eastern Himalayan region of northeast India. The wild populations of citron in the region have undergone rapid decline due to natural and anthropogenic disturbances and most of the remaining individuals of citron are found in fragmented natural forests and home gardens in the region. In order to assess the genetic structure and diversity of citron in wild and domesticated populations, we analyzed 219 individuals of C. medica collected from four wild and eight domesticated populations using microsatellite markers. The genetic analysis based on five polymorphic microsatellite loci revealed an average of 13.40 allele per locus. The mean observed and expected heterozygosity values ranged between 0.220–0.540 and 0.438–0.733 respectively among the wild and domesticated populations. Domesticated populations showed close genetic relationships as compared to wild populations and pairwise Nei's genetic distance ranged from 0.062 to 2.091 among wild and domesticated populations. Analysis of molecular variance (AMOVA) showed higher genetic diversity among‐ than within populations. The analysis of population structure revealed five groups. Mixed ancestry of few individuals of different populations revealed exchange of genetic materials among farmers in the region. Citron populations in the region show high genetic variation. The knowledge gained through this study is invaluable for devising genetically sound strategies for conservation of citron genetic resources in the region.