High colonization by native arbuscular mycorrhizal fungi (AMF) of rubber trees in small-holder plantations on low fertility soils in North East Thailand

Rubber tree is a very important crop in Thailand, representing an essential source of income for farmers. In the past two decades, rubber tree plantations have been greatly expanding in unfavorable areas, where climate conditions are difficult and soil fertility is very poor. To optimize latex yields, mineral fertilizers have been widely used. A better understanding of the roles of the biological compartment in soil fertility is essential to determine alternative management practices to sustain soil fertility and optimize latex yields. Arbuscular mycorrhizal fungi (AMF) are widely recognized as beneficial for plants, mainly through their role in improving plant nutrient uptake. The objective of this study was to assess the AMF populations in rubber tree plantations and the impact of both soil characteristics and plantation age on these communities. Our results showed that all rubber trees were highly colonized, regardless of the soil structure and nutrient contents. AMF colonization was not affected by the age of the trees, suggesting that maintaining the symbiosis is likely to be beneficial at all stages. A better understanding and management of the microbial communities would contribute to maintaining or restoring soil fertility, leading to a better tree growth and optimized latex yield.

Diversity of root-associated arbuscular mycorrhizal fungal communities in a rubber tree plantation chronosequence in Northeast Thailand

Rubber tree (Hevea brasiliensis) is of major economic importance in Southeast Asia and for small land holders in Thailand in particular. Due to the high value of latex, plantations are expanding into unsuitable areas, such as the northeast province of Thailand where soil fertility is very low and therefore appropriate management practices are of primary importance. Arbuscular mycorrhizal fungi (AMF) contribute to plant growth through a range of mechanisms and could play a key role in a more sustainable management of the rubber plantations. We described the diversity of AMF associated with rubber tree roots in Northeast Thailand in relation to tree age and soil parameters along a chronosequence of rubber tree plantations. Cassava fields were included for comparison. Rubber tree and cassava roots harbored high diversity of AMF (111 Virtual Taxa, VT), including 20 novel VT. AMF VT richness per sample was consistently high (per site mean 16 to 21 VT per sample) along the chronosequence and was not related to soil properties. The composition of AMF communities differed between cassava and rubber tree plantations and was influenced by soil texture and nutrient content (sand, K, P, Ca). AMF community composition gradually shifted with the age of the trees. Our results suggest that the high diversity of AMF in this region is potentially significant for maintaining high functionality of AMF communities.

Variation in Cyclaneusma minus isolates

Cyclaneusma minus is a plant pathogen that has financial impacts on the forestry industry. This study characterised the genetic variation in Australian and New Zealand isolates of Cyclaneusma minus using both molecular and morphological techniques and developed a PCR detection test for the presence of Cyclaneusma minus in tree plantations.

Conservation of tropical forest tree species in a native timber plantation landscape

Tropical terrestrial environments are becoming dominated by anthropogenic land-uses, making retention of biodiversity in production landscapes of critical conservation importance. Native timber plantations may represent a land-use capable of balancing production and conservation by potentially supporting understorey plant and tree species otherwise restricted to old-growth forests, with little impact on yield. In this study we investigated the conservation value of native plantation forests in the lowlands of New Britain, Papua New Guinea. We compared the composition of tree species (≥10. cm DBH) of unlogged forest to those of different aged native Eucalyptus deglupta plantations and intervening (historically logged) secondary forests. We found a high capacity for biodiversity conservation within plantations, with 70% of forest tree species persisting in mature plantations (13-15. years old). However, compositional analyses revealed lower numbers of large individuals (≥10. cm DBH) in both late-successional and non-vertebrate-dispersed species in the plantations, indicating the difficulty of retaining mature old-growth forest trees in production land-uses. Secondary forest protected by conservation reserves was compositionally indistinct to unlogged forest. Our results demonstrate the potential for tropical native timber plantations to contribute to the retention of biodiversity. However, appropriate management is required to ensure the persistence of source populations of old-growth forest tree species. With careful planning a balance between production and conservation can be achieved in lowland tropical regions.