Absence of aluminium compromises root integrity,reduces leaf hydration and Rubisco performance in Qualea grandiflora,an Al-accumulating species

• Aluminium (Al) is toxic to most plants. Nevertheless, some species accumulate Al without showing toxicity symptoms. Previous studies have evidenced Al in chloroplasts of Al-accumulating species from the Cerrado vegetation in South America. We ask whether Al increases carbon assimilation through enhanced apparent efficiency of Rubisco.
• Seedlings of the Al-accumulator Qualea grandiflora (Vochysiaceae) were grown in nutrient solution with 0, 740, and 1480 μm Al. Growth parameters, relative leaf water content, Al concentration in organs, gas exchange and apparent carboxylation efficiency (measured from A/Ci curves) were evaluated for 60 days.
• Plants without Al showed no root growth, necrotic roots, low gas exchange rates, and decreased apparent carboxylation efficiency. Al-treated plants, however, showed new white roots and increased root biomass leading to higher leaf hydration, and apparent carboxylation efficiency was higher in these plants. Increased Al available in the nutrient solution increased Al accumulation in plant organs.
• Absence of Al compromised root integrity in Q. grandiflora, thus limiting leaf hydration. No positive direct effect of Al on Rubisco was evidenced in Al-treated plants.

     

How widespread is woody plant encroachment in temperate Australia? Changes in woody vegetation cover in lowland woodland and coastal ecosystems in Victoria from 1989 to 2005

Aim Encroachment or densification by woody plants affects natural ecosystems around the world. Many studies have reported encroachment in temperate Australia, particularly in coastal ecosystems and grassy woodlands. However, the degree to which published studies reflect broad-scale changes is unknown because most studies intentionally sampled areas with conspicuous densification. We aimed to estimate changes in woody vegetation cover within lowland grassy woodland and coastal ecosystems in Victoria from 1989 to 2005 to determine whether published reports of recent encroachment are representative of broad-scale ecosystem changes. Location All lowland grassy woodland and coastal ecosystems (c. 6.11 × 10⁵ ha) in Victoria, Australia. Four major ecosystems were analysed: Plains woodlands, Herb-rich woodlands, Riverine woodlands and Coastal vegetation. Methods Changes in woody vegetation cover from 1989 to 2005 were assessed based on state-wide vegetation maps and Landsat analyses of woody vegetation cover conducted by the Australian Greenhouse Office’s National Carbon Accounting System. The results show changes in woody cover within mapped patches of native vegetation, rather than changes in the extent of woody vegetation resulting from clearing and revegetation. Results When pooled across all ecosystems, woody vegetation increased by 18,730 ha from 1989 to 2005. Woody cover within Riverine woodlands and within Plains woodlands each increased by >7000 ha. At the patch scale, the mean percentage cover of woody vegetation in each polygon increased by >5% in all four ecosystems: Riverine woodlands (+9.2% on average), Herb-rich woodlands (+7.6%), Plains woodlands (+6.7%) and Coastal vegetation (+5.9%). Regression models relating degree of encroachment to geographic and climatic variables were extremely weak (r² ≤ 0.026), indicating that most variation occurred at local scales rather than across broad geographic gradients. Main conclusions At the scale of observation, woody vegetation cover increased in all lowland woodland and coastal ecosystems over the 16-year period. Thus, published examples of encroachment in selected coastal and woodland patches do appear to reflect widespread increases in woody vegetation cover in these ecosystems. This densification appears to be associated with changes in land management rather than with post-fire vegetation recovery and is likely to be ongoing and long-lasting, with substantial implications for biodiversity conservation and ecosystem services.     

Impact of encroaching woody vegetation on nest success of upland nesting waterfowl

Grassland managers often regard woody vegetation as hostile habitat that potentially reduces the abundance and fecundity of wildlife that use grasslands. We tested that assumption for waterfowl by examining patterns of nest success on study areas that differed in current extent and previous management of woody vegetation. We located and monitored 1,064 waterfowl nests on 33 federally owned Waterfowl Production Areas (WPAs) in western Minnesota during 2008–2010. Sites contained 0.3–15.1% woodland and also varied markedly in extent of shrubs and scattered trees. Average nest success was low (12.9%), but ranged from 1.5% to 38.7% among site-years. Nests were more likely to succeed when located in landscapes containing more grass (500-m scale) and fewer wetlands (100-m scale), but none of 8 variables measuring woody vegetation were negatively associated with nest survival and 1 variable (abundance of lone trees) was positively associated with nest survival. Our results indicate that management efforts focusing on removing woody vegetation are unlikely to provide improvements in nest survival rates for breeding waterfowl, except to the extent that such management is necessary to maintain large tracts of grassland. © 2012 The Wildlife Society.     

Local and landscape‐scale effects of an ant nest construction in an open dry forest of Uruguay

1. Ants modify soil properties via nest construction and by doing this modulate soil resources for other organisms. In this sense ants are recognised as ecosystem engineers. 2. In this framework, two less well‐studied issues are focused on: (i) the permanence of the effects of ant nests on plant communities after colonies have died, and (ii) the scaling up from patch to landscape‐scale effects. 3. The aim of the present study was to address these issues in the open dry forests of Uruguay, inhabited by the ant Atta vollenweideri Forel. The active and abandoned nests of this ant represent different and conspicuous patches (30–60 m²) in the landscape. 4. The soil concentration of sodium, a key element in the system, was substantially higher among active nests, and remains high during the early stages of abandoned nests. Woody species abundance, richness, and composition were affected at the patch scale, and simulation models suggested an increase in species richness at the landscape scale. 5. The present study highlights the importance of abandoned nests for plant‐species richness in the ecosystem engineer framework and the need to advance in an integrative approach to study both local and landscape effects of ant's nests.     

How does the richness of wood-decaying fungi relate to wood microclimate?

Microclimatic conditions in dead wood influence fungal growth and hence also species composition, but it remains unclear how they influence species richness in nature. We analysed fungal species richness based on the occurrence of fruit bodies on 2 m long segments of both standing and lying trunks of Norway spruce (Picea abies). The number of non-red-listed species was related positively to moisture, and negatively to both temperature extremes and fluctuations. The numbers of both red-listed and non-red-listed species were further differently influenced by trunk diameter and by trunk properties related to the progression in wood decay. These results indicate that the richness of fungal communities in dead wood is shaped by an interaction of wood decay, moisture and temperature fluctuations.     

Vegetation factors influencing density and distribution of wild large herbivores in a southern African savannah

Understanding factors influencing large herbivore densities and distribution in terrestrial ecosystems is a fundamental goal of ecology. This study examined environmental factors influencing the density and distribution of wild large herbivores in Gonarezhou National Park, Zimbabwe. Vegetation and surface water were predicted to have a stronger influence than anthropogenic‐related disturbances (livestock grazing, fires, settlements and poaching) on the density and distribution of wild large herbivores. Aerial survey data for seven common wild large herbivores conducted in 2007 and 2009 and environmental data were collected. Only grass cover explained a significant proportion of the variation in large herbivore densities and distribution. Moreover, only two species densities significantly differed across the Gonarezhou, namely impala and zebra. In contrast, buffalo, elephant, giraffe, kudu and nyala densities did not differ significantly across the Gonarezhou. Overall, the findings only partly support the study prediction. The study results suggest the need to further investigate the roles of environmental factors at smaller scales in order to tease out their relative strengths in influencing density and distribution of large herbivores.     

A Unified Law of Spatial Allometry for Woody and Herbaceous Plants

Abstract: The objective of the present paper is to provide both proof and theoretical deduction of an overlapping, valid law of allometry for woody and herbaceous plants used in agriculture and forestry. In his attempt to find an adequate expression for stand density, independent of site quality and age, Reineke (1933^[281]) developed the following equation for even‐aged and fully stocked forest stands in the northwest of the USA: ln(N) = a ‐ 1.605 . ln(dg), based on the relationship between the average diameter dg and the number N of trees per unit area. With no knowledge of these results, Kira et al. (1953^[281]) and Yoda et al. (1957^[281] and 1963^[281]) found the boundary line ln(m) = b ‐ 3/2 . ln(N) in their study of herbaceous plants. This self‐thinning rule ‐ also called the ‐ 3/2‐power rule ‐ describes the relationship between the average weight m of a plant and the density N in even‐aged herbaceous plant populations growing under natural development conditions. It is possible to make a transition from Yoda's rule to Reineke's stand density rule if mass m in the former rule is substituted by the diameter dg. From biomass analyses for the tree species spruce (Picea abies [L.] Karst.) and beech (Fagus sylvatica L.), allometric relationships between biomass m and diameter d are derived. Using the latter in the equation ln(m) = b ‐ 3/2 . ln(N) leads to allometric coefficients for spruce (Picea abies [L.] Karst.) and beech (Fagus sylvatica L.), that come very close to the Reineke coefficient. Thus Reineke's rule (1933^[281]) proves to be a special case of Yoda's rule. Both rules are based on the simple allometric law governing the volume of a sphere v and its surface of projection s: v = c₁ . s^3/2. If the surface of projection s, is substituted by the reciprocal value of the number of stems s = 1/N and the isometric relationship between volume v and biomass m is considered v = c₂ . m^1.0 we come to Yoda's rule m = c₃ . N^‐3/2 or, in logarithmic terms, ln(m) = ln c₃ ‐ 3/2 . ln(N).