Differences of the stem vascular system across populations of two tropical species under contrasting water conditions

Structural differences in the secondary vascular tissues among habitats can contribute to understanding species performances, especially regarding water and photosynthate transport. The pattern of association between the secondary xylem tissue and water availability from the environment has been widely studied, unlike the secondary phloem, which has been barely explored. Here, we evaluated the structural variation of the secondary xylem and phloem in stems of four populations of two tropical tree species under contrasting water conditions. We also investigated the mirrored structure between both tissues. At dry sites, Moquiniastrum polymorphum had higher vessel density, thicker xylem fibers cell walls, and taller rays in both tissues commonly associated with safe transport, in agreement with our expectations. In contrast, the populations of Zanthoxylum rhoifolium had most features in disagreement with the water availability of each site. The perforation and sieve plates, the ray composition, and the axial parenchyma were similar in the two tree species’ xylem and phloem tissues. However, the quantitative descriptors of cell sizes were not correlated between the xylem and phloem. In general, there is a different pattern of morphological variation across sites in the two tropical tree species, highlighting that any generalization regarding the vascular system structure across environments should be avoided. Xylem and phloem revealed a mirrored structure in a few qualitative features, not followed by the dimensions of different cell types. Future research needs to explore the causes of the unexpected structural variation in the vascular system across populations in tropical tree species.

The genetic diversity of angsana (Pterocarpus indicus) in Purwodadi Botanical Garden Indonesia revealed by rDNA ITS

Pterocarpus indicus or angsana is one of the tropical tree species that produce redwood. It has been listed as an endangered species by IUCN since 2018, as its natural population number has declined and possibly extinct in some countries. Therefore, conservation efforts to protect this species must be carried out based on the appropriate conservation strategy. This study aimed to assess molecular characters of Pterocarpus species in Purwodadi Botanical Garden using rDNA ITS (internal transcribed spacer) and its association with morphological characters. Information on genetic and morphological characters will precisely identify this species so that conservation strategy can be appropriately planned. Leaf samples of eighteen P. indicus trees were collected from Purwodadi Botanical Garden (PBG) and used in this study. Twelve specimens that provide clear DNA sequence were genetically assessed. The results showed that P. echinatus exhibited rDNA ITS character similar to that P. indicus, while P. indicus specimens from Morotai were very different from other P. indicus specimens. Morotai specimens showed 89% similarity to several Pterocarpus species, including P. acapulcensis, P. rohrii and P. indicus. The morphological characters were assessed along with molecular characters. The impacts of conservation strategies are discussed in this paper.

Conservation and sustainable utilization of tropical trees from North Sumatra, Indonesia

Tree species have received more attention recently due to its contribution and prospective utilization. Although provided many function for human and ecosystem, the existence of trees also threatened due to illegal harvesting and forest conversion. Sustainable utlization approaches were needed for increasing the value and willingness of the community to engage in conservation activities. Although many tropical tree species, especially in North Sumatra, have been exploited, there are still few reports of sustainable approaches to those species. In this study, the assessment of several local tree species in North Sumatra was approached with five conditions adopted from previous research, those were :1) sustainable harvesting, (2) no threat interaction, (3) effective commercialization, (4) economic benefits to farmers, and 5) utilization of financial proceeds to promote conservation initiatives. The results of the study illustrate that although these four criteria are fulfilled, the forest product trade often does not provide sufficient financial benefits to protect forests from other threats. Therefore, it is necessary to understand the interaction between threats for sustainable use and conservation, by using a precise conceptual model. The financial benefits of sustainable use must be adequate to support conservation efforts that can overcome various threats to tree species conservation.

Variation in Onset of Leaf Unfolding and Wood Formation in a Central African Tropical Tree Species

A diversity of phenological strategies has been reported for tropical tree species. Defoliation and seasonal dormancy of cambial activity inform us on how trees cope with water stress during the dry season, or maximize the use of resources during the rainy season. Here, we study the matching between leaf phenology (unfolding and shedding) and cambial activity for Prioria balsamifera, a key timber species in the Democratic Republic of Congo. In particular, we (i) evaluated the seasonality of cambial activity and synchrony of phenology among trees in response to climate and (ii) identified the seasonality of leaf phenology and its relation with cambial phenology. The study was conducted in the Luki Man and Biosphere Reserve, located in the Mayombe forest at the southern margin of the Congo Basin. Historic defoliation data were collected every ten days using weekly crown observations whereas recent observations involved time-lapse cameras. Cambial pinning was performed on ten trees during 20 months and radius dendrometers were installed on three trees during 13 months. Tree rings were measured on cores from 13 trees and growth synchrony was evaluated. We found that P. balsamifera defoliates annually with a peak observed at the end of the dry season and the beginning of the rainy season. The new leaves unfolded shortly after shedding of the old leaves. The peak defoliation dates varied across years from September 12 to November 14 and the fraction of number of trees that defoliated at a given time was found to be negatively correlated with annual rainfall and temperature; during the dry season, when precipitation and temperatures are the lowest. Wood formation (radial growth), was found to be highly seasonal, with cambial dormancy occurring during the dry season and growth starting at the beginning of the rainy season. Individual ring-width series did not cross date well. The within species variability of leaf phenology and cambial rhythms provides indication about resistance of the population against climatic changes.

In vitro Methane Mitigation Potential of Foliage of Fodder Trees Mixed at Two Levels with a Tropical Grass

Enteric methane (CH4) emitted by ruminant species is known as one of the main greenhouse gases produced by the agricultural sector. The objective of this study was to evaluate the chemical composition, in vitro gas production, dry matter degradation (DMD), digestibility, CO2 production and CH4 mitigation potential of five tropical tree species with novel forage potential including: Spondias mombin, Acacia pennatula, Parmentiera aculeata, Brosimum alicastrum and Bursera simaruba mixed at two levels of inclusion (15 and 30%) with a tropical grass (Pennisetum purpureum). Crude protein content was similar across treatments (135 g kg-1 DM), while P. purpureum was characterized by a high content of acid detergent fiber (335.9 g kg-1 DM) and B. simaruba by a high concentration of condensed tannins (20 g kg-1 DM). Likewise, A. pennatula and P. aculeata were characterized by a high content of cyanogenic glycosides and alkaloids respectively. Treatments SM30-PP70 (30% S. mombin + 70% P. purpureum) and BA30-PP70 (30% B. alicastrum + 70% P. purpureum) resulted in superior digestibility than P. purpureum, while in the AP30-PP70 (30% A. pennatula + 70% P. purpureum) was lower than the control treatment (P≤0.05). At 24 and 48 h, treatments that contained P. aculeata and B. alicastrum produced higher CH4 ml g-1 DOM than P. purpureum (P≤0.05). The inclusion of B. simaruba at 30% reduced CH4 at 25% compared to P. purpureum. Tropical tree species can improve the nutritional quality of ruminant rations and reduce CH4 emissions to consequently contribute to the development of sustainable ruminant production systems that generate diverse ecosystem services.