Nodulation of native woody legumes in Hong Kong, China

Abstract

Woody legumes can play an important role in forest restoration on degraded land but the knowledge of woody legumes has lagged behind their uses. This study is a pioneer investigation to explore the ability of native woody legumes to form root nodules and fix nitrogen in Hong Kong. Nine sites of different habitat types were surveyed during both wet and dry seasons for two years. Young plants of woody legumes along studied transects were excavated. The patterns of nodulation and nodule morphology were recorded and the nitrogen fixing ability was tested by acetylene-reduction-assay. Twentyeight species in 16 genera were examined, of which 20 species were nodulating and eight non-nodulating, including all six species in the Caesalpinioideae. Five species were new records to the world's nodulation inventory. Bowringia callicarpa was a new species and genus examined, which was non-nodulating. The overall nodulation pattern was consistent with previous studies. Nodulation was more profuse in some shrub species while inconsistent in most tree species. Species with higher proportion of nodulated individual plants also tended to have more nodules in each plant.Spherical nodules were common in shrub and woody climber species whilst tree species usually had woody indeterminate nodules. Seasonal difference in the amount of senescent nodules was noted in most species. All the nodules tested by acetylene-reductionassay were effectively nitrogen-fixing, with nitrogenase activity ranging from 4 μmol C 2 H 4 g −1 h −1 to 20 μmol C 2 H 4 g −1 h −1 , which was comparable to other tropical tree species. The findings in nodulation pattern and nitrogen fixing ability of these species are essential in their application in forest restoration on degraded lands.

Nodulation in the Legume Biofuel Feedstock Tree Pongamia pinnata

“…These coralloid nodules are hypothesised to be older nodules that have become partially indeterminate and are exhibiting new bacterial colonisation and nodule cell division. It has been previously noted in several studies that most tree legumes tend to have woody indeterminate nodules [3,28,34]. We conclude that pongamia nodulation at first leads to determinate-type nodules and often progresses later into an indeterminate state.…”

“…As previously mentioned, indeterminate nodules are to be found on most woody legumes. A survey of wild legumes in China by Ng and Nau [28] observed spherical nodules on all legume species; however, these nodules were thought to be undifferentiated and immature, if nodules of other shapes were also observed. This idea of globular nodules turning into cylindrical indeterminate nodules is not new.…”

Do N‐fixing legumes promote neighbouring diversity in the tropics?

“…This complicates the precise evaluation of %Ndfa (Boddey et al, ; Unkovich, ; Unkovich et al, ). Therefore, we validated the method by comparing our results with published data of nitrogenase activity by Ng and Hau (). Comparisons showed that %Ndfa appeared to be a good proxy for BNF ability, as for the majority of the legumes the difference in δ 15 N with their neighbours was significant and consistent with laboratory analysis of nitrogenase activity by Ng and Hau ().…”

“…Biological nitrogen fixation (BNF) by legumes is considered a major source of soil nitrogen (N), in addition to atmospheric deposition (Galloway et al, ), bacterial and fungal nitrification (Peix, Ramírez‐bahena, Velázquez, Peix, & Ram, ) and geochemical weathering (Holloway & Dahlgren, ). Much research has been carried out to quantify and understand BNF in both natural (Ng & Hau, ; Nichols, Rosemeyer, Carpenter, & Kettler, ; Vitousek, Menge, Reed, & Cleveland, ) and agricultural systems (Unkovich et al, ). For example, by intercropping, N‐fixing soybeans can supply N to adjacent plants directly via root exudates and root decomposition and further facilitate phosphorus (P) mobilization by mycorrhizal activities (Govindarajulu et al, ; Klein, Siegwolf, & Körner, ; Liu, Wu, Baddeley, & Watson, ; Mulder, Jumpponen, Högberg, & Huss‐Danell, ; Paynel, Murray, & Cliquet, ).…”

“…However, the role of legumes is less clear in natural forests. For example, the factors that govern nodulation and the distribution of legume tree species have been much debated (Diabate et al, ; Moreira, Silva, & Faria, ; Ng & Hau, ; Sprent, ).…”