Investigations on decomposition of foliage of woody species using a perfusion method

The time for half of the total oxidizable carbon to be converted into CO₂ and other gaseous products (t_1/2) was studied for five tree species used in agroforestry. The study was conducted in a perfusion system with continuous aeration, and moisture content maintained at field capacity. This method was found to be suitable for studies of the initial stages of tree foliage decomposition. The overall rate was in the decreasing order: Leucaena>Calliandra>Gliricidia>Prosopis>Cassia. Decomposition started rapidly and then decreased rapidly for 2 to 3 weeks followed by a gradual decrease which continued for the remainder of the time.The time for 50 per cent of total oxidizable carbon to decompose was about 19 days for Leucaena, 30 days for Calliandra and Gliricidia, while Prosopis and Cassia took more than 30 days. Leucaena released the largest quantity of total N into the perfusing solution while Cassia gave the lowest amount.     

Towards an ontogenetic understanding of inflorescence diversity

Backgrounds and Aims

Conceptual and terminological conflicts in inflorescence morphology indicate a lack of understanding of the phenotypic diversity of inflorescences. In this study, an ontogeny-based inflorescence concept is presented considering different meristem types and developmental pathways. By going back to the ontogenetic origin, diversity is reduced to a limited number of types and terms.

Methods

Species from 105 genera in 52 angiosperm families are investigated to identify their specific reproductive meristems and developmental pathways. Based on these studies, long-term experience with inflorescences and literature research, a conceptual framework for the understanding of inflorescences is presented.

Key Results

Ontogeny reveals that reproductive systems traditionally called inflorescences fall into three groups, i.e. ‘flowering shoot systems’ (FSS), ‘inflorescences’ sensu stricto and ‘floral units’ (FUs). Our concept is, first, based on the identification of reproductive meristem position and developmental potential. The FSS, defined as a seasonal growth unit, is used as a reference framework. As the FSS is a leafy shoot system bearing reproductive units, foliage and flowering sequence play an important role. Second, the identification of two different flower-producing meristems is essential. While ‘inflorescence meristems’ (IMs) share acropetal primordia production with vegetative meristems, ‘floral unit meristems’ (FUMs) resemble flower meristems in being indeterminate. IMs produce the basic inflorescence types, i.e. compound and simple racemes, panicles and botryoids. FUMs give rise to dense, often flower-like units (e.g. heads). They occur solitarily at the FSS or occupy flower positions in inflorescences, rendering the latter thyrses in the case of cymose branching.

Conclusions

The ontogenetic concept differs from all existing inflorescence concepts in being based on meristems and developmental processes. It includes clear terms and allows homology statements. Transitional forms are an explicit part of the concept, illustrating the ontogenetic potential for character transformation in evolution.     

Non‐timber Forest Product Harvest does not Affect the Genetic Diversity of a Tropical Tree Despite Negative Effects on Population Fitness

The level of genetic diversity in a population can affect ecological processes and plant responses to disturbance. In turn, disturbance can alter population genetic diversity and structure. Populations in fragmented and logged habitats often show reduced genetic diversity and increased inbreeding and differentiation. Long‐term harvesting of wild plants (for foliage, bark, and roots), can affect population genetic diversity by altering individual fitness and genetic contribution. Our understanding of these changes in genetic diversity due to the harvesting of plant organs is still limited. We used nine microsatellite markers to study the effect of long‐term bark and foliage harvest by Fulani people on the genetic diversity and structure of 12 populations of African mahogany (Khaya senegalensis) in Benin. We sampled 20 individuals in each population to test the effect of harvesting. For each population, we divided the samples equally between seedling and adults to test if the effects are stronger in seedlings. We found moderate genetic diversity (H_e = 0.53 ± 0.04) and weak but significant differentiation among local populations (F_ST = 0.043, P < 0.001). There was no significant effect of harvest on genetic diversity or structure, although previous work found significant negative effects of harvest on the reproduction of adults, offspring density, and population fitness. Our results suggest that demographic responses to disturbance precede a detectable genetic response. Future studies should focus on using parentage analysis to test if genotypes of harvested parents are directly represented in the offspring populations.     

Growth and uptake of N,P, K and B by Pinus radiata D. Don in response to applications of borax

Leader dieback associated with B deficiency in P. radiata D. Don plantations was treated with borax applied at rates of 50, 100 and 150 kg ha⁻¹. This initially increased B in foliage from 5 to 40, 80 and 110 μg g⁻¹ respectively, and was followed by a rapid decline and stabilisation at around 25 μg g⁻¹ for the duration of the study. Annual fluctuations in foliage B levels were strongly correlated with rainfall during the preceding spring and summer. Uptake of N, P and K increased as a result of applied B and comparison of the distribution of these nutrients in crowns of fertilized and unfertilised trees six years after application indicated continued uptake of these nutrients probably as a result of improved root growth due to B. Foliage concentrations of B like N, P and K, increased in young needles towards the upper crown and this, together with a decline in needle concentrations of B as foliage aged, indicated some redistribution of B from older to new foliage. A limit of 5 μg g⁻¹ was found below which little redistribution seems to occur. Application of B prevented further leader dieback, improved apical dominance and height growth and increased volume production by 25 m³ ha⁻¹ at age 8 years. Differences between application rates of B were not significant in terms of growth.     

Effects of leaf damage on oviposition choice in an invasive paropsine beetle

In 2007, an invasive paropsine beetle, Paropsisterna nr. gloriosa Blackburn, caused severe defoliation of Eucalyptus in mixed‐species foliage plantations in south‐west Ireland. At many of the plantations, Eucalyptus parvula L.A.S. Johnson & K.D. Hill was the most heavily damaged species while Eucalyptus pulverulenta Sims was generally resistant to the beetle. However, at the most heavily damaged site beetles moved to feed on E. pulvarulenta presumably during periods when suitable foliage (new leaves) of E. parvula had been severely depleted. The present study examines factors underlying shifts in oviposition from the preferred to non‐preferred host. In choice and no‐choice experiments, P. nr. gloriosa laid more eggs directly on new E. parvula foliage compared with new E. pulverulenta foliage. However, in choice experiments where new E. parvula foliage was unavailable (but old foliage available), more eggs were laid on new E. pulverulenta foliage. The potential for prior feeding damage to stimulate or deter oviposition on either host was also examined. Prior damage to new and old E. parvula leaves increased egg‐laying directly on the damaged foliage; however, prior damage to E. pulverulenta may have inhibited oviposition. The results suggest that in mixed‐species plantations, facilitation of oviposition on preferred hosts through prior feeding damage helps maintain the relative resistance of E. pulverulenta against P. nr. gloriosa, even under high beetle densities. However, the vulnerability of E. pulverulenta will increase where suitable age‐classes of preferred‐host foliage are severely depleted or unavailable.     

Canopy dynamics estimated from shoot morphology in an evergreen broad-leaved forest

Summary A forest canopy structure may be defined as the spatial distribution pattern of foliage density, and dynamics of canopy can be considered as changes of spatial distribution of foliage density. To study this process, the annual intrinsic growth factor (r) of foliage and the speed with which foliage shifts its position were estimated from shoot branching and shoot length. The spatial distributions of these parameters were obtained from a profile of evergreen broad-leaved forest. r was large in the upper canopy layer and canopy gap; this indicated the active development of foliage. This phenomenon may be a major reason for the existence of dense foliage in the upper canopy. The speed with which foliage shifts its position was high in the canopy gap. For dominant species, light conditions affected positively on the distribution of r.