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Potential growth and drought tolerance of eight desert grasses: lack of a trade-off? (2000)

Fernández, R. J. ; Reynolds, J. F.

Springer

Oecologia 123 (2000), S. 90-98

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ISSN: 1432-1939

Keywords: Key words Chihuahuan Desert ; C-4 photosynthesis ; Water stress ; Relative growth rate ; Xerophytism

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Eight perennial C-4 grasses from the Jornada del Muerto Basin in southern New Mexico show five-fold differences in relative growth rates under well- watered conditions (RGRmax). In a controlled environment, we tested the hypothesis that there is an inverse relationship (trade-off) between RGRmax and the capacity of these species to tolerate drought. We examined both physiological (gas exchange) and morphological (biomass allocation, leaf properties) determinants of growth for these eight species under three steady-state drought treatments (none=control, moderate, and severe). When well watered, the grasses exhibited a large interspecific variation in growth, which was reflected in order-of-magnitude biomass differences after 5 weeks. The species had similar gas-exchange characteristics, but differed in all the measured allocation and morphological characteristics, namely tiller mass and number, root:shoot ratio, dry-matter content, and specific leaf area (SLA). Drought affected tillering, morphology, and allocation, and reduced growth by 50 and 68% (moderate and severe drought, respectively) compared to the well-watered controls. With the exception of SLA, none of these variables showed a significant species-by-treatment interaction. We calculated three indices of drought tolerance, defined as the ratio in final biomass between all the possible ”dry”/”wet” treatment pairs: severe/moderate, moderate/control, and severe/control. We found no significant correlation between these drought tolerance indices, on the one hand, and three indices of growth potential (greenhouse RGRmax, final biomass in the control treatment, and final:initial biomass ratio in controls), on the other. Based on these controlled-environment results, we hypothesize that the commonly reported correlation between plant growth potential and drought tolerance in the field may in some cases be explained by differential effects of plants on soil-water content rather than by differences in species responses to drought.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004420050993

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Contrasting demography of two Patagonian shrubs under different conditions of sheep grazing and resource supply (1992)

Fernández, R. J. ; Nuñez, A. H. ; Soriano, A.

Springer

Oecologia 91 (1992), S. 39-46

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ISSN: 1432-1939

Keywords: Grazing ; Life histories ; Patagonia ; Resource levels ; Shrubs

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Two shrub species, dominant in western Patagonia, Argentina, exhibited different demographic behaviors under the effect of sheep grazing and of manipulated resource levels. Senecio filaginoides showed an increase in cover under increasing grazing pressures; the rise was explained by an increasing number of individuals and not by larger plants; this trend was reversed when no grazing took place. Mulinum spinosum showed a slight decrease in cover and density at increasing grazing pressures, and no change in plant size. In a field experiment in which water was added (30 mm in early summer) and the dominant grasses removed, both factors substantially augmented the number of 1-year-old seedlings of Senecio recruited; the only noticeable response of Mulinum was an increase in seedling emergence because of grass removal. Six years after this last treatment, Senecio exhibited a ten fold increase in density, and its population structure showed a peak in younger classes; Mulinum remained unaffected. In seedling surveys conducted within an exclsure and in its surroundings, the emergence of Senecio was similar in these areas in the two years of the study, whereas the emergence of Mulinum was higher inside the exclosure for one of the years. The emergence of Senecio in the wetter year was 3 times larger than in the drier one. Grazing did not affect first-year survival of any species; the major source of seedlign death in this case, as well as in the manipulative experiment, was desiccation during summer drought. We conclude that the contrasting responses of the two species to grazing are mostly due to the greater ability of Senecio to benefit from any increase in resources, including those not used by grazed plants. The difference might also be due to a reduction in the seed availability of Mulinum caused by sheep preference for its fruits. The dissimilar abilities of the two shrubs to employ the resources freed by grazing would derive more from their contrasting demographic potential (i.e. the ability to rapidly increase biomass/m2) than from a difference in their niche overlap with palatable species.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00317238

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Growth potential limits drought morphological plasticity in seedlings from six Eucalyptus provenances (2016)

Maseda, P. H., Fernandez, R. J.

Oxford University Press

In: Tree Physiology

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Publication Date: 2016-02-20

Description: Water stress modifies plant above- vs belowground biomass allocation, i.e., morphological plasticity. It is known that all species and genotypes reduce their growth rate in response to stress, but in the case of water stress it is unclear whether the magnitude of such reduction is linked to the genotype's growth potential, and whether the reduction can be largely attributed to morphological adjustments such as plant allocation and leaf and root anatomy. We subjected seedlings of six seed sources, three from each of Eucalyptus camaldulensis (potentially fast growing) and E. globulus (inherently slow growing), to three experimental water regimes. Biomass, leaf area and root length were measured in a 6-month glasshouse experiment. We then performed functional growth analysis of relative growth rate (RGR), and aboveground (leaf area ratio (LAR), specific leaf area (SLA) and leaf mass ratio (LMR)) and belowground (root length ratio (RLR), specific root length (SRL) and root mass ratio (RMR)) morphological components. Total biomass, root biomass and leaf area were reduced for all Eucalyptus provenances according to drought intensity. All populations exhibited drought plasticity, while those of greater growth potential (RGR max ) had a larger reduction in growth (discounting the effect of size). A positive correlation was observed between drought sensitivity and RGR max . Aboveground, drought reduced LAR and LMR; under severe drought a negative correlation was found between LMR and RGR max . Belowground, drought reduced SRL but increased RMR, resulting in no change in RLR. Under severe drought, a negative correlation was found between RLR, SRL and RGR max . Our evidence strongly supports the classic ecophysiological trade-off between growth potential and drought tolerance for woody seedlings. It also suggests that slow growers would have a low capacity to adjust their morphology. For shoots, this constraint on plasticity was best observed in partition (i.e., LMR) whereas for roots it was clearest in morphology/anatomy (i.e., SRL). Thus, a low RGR max would limit plastic response to drought not only at the whole plant level but also at the organ and even the tissue level.

Print ISSN: 0829-318X

Electronic ISSN: 1758-4469

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition