Gabriel Montserrat-Martí

Stem xylem features in three Quercus (Fagaceae) species along a climatic gradient in NE Spain

Abstract Stem xylem features in two evergreen Quercus species (Q. coccifera and Q. ilex) and a deciduous one (Q. faginea) were analysed along an Atlantic-Mediterranean climatic gradient in which rainfall and winter cold experience strong variation. Mean maximum vessel diameter, vessel density, vessel element length, xylem transverse sectional area, Huber value (xylem transverse sectional area per leaf area unit), theoretical leaf specific conductivity (estimated hydraulic conductance per leaf area unit) and total leaf area were determined in 3-year-old branches. Q. faginea presented the widest vessels and the highest theoretical leaf specific conductivity while Q. coccifera showed the lowest total leaf area and the highest Huber value. Studied features did not exhibit significant correlations with mean minimum January temperature in any species but did show significant relationships with rainfall. In Q. coccifera, mean maximum vessel diameter, vessel element length and theoretical leaf specific conductivity increased with higher rainfall while vessel density decreased. Mean maximum vessel diameter and total leaf area in Q. ilex increased with precipitation whereas variables of Q. faginea did not show any significant trend. Results suggest that aridity, rather than minimum winter temperature, controls stem xylem responses in the studied evergreen species. Q. faginea traits did not show any response to precipitation, probably because this species develops deep roots, which in turn makes edaphic and topographic factors more important in the control of soil water availability. In response to aridity Q. coccifera only exhibits adjustment at a xylem level by reducing its water transport capacity through a reduction of vessel diameter without changing the amount of xylem tissue or foliage, whereas Q. ilex adjusts its water transport capacity in parallel to the foliage area.

Leaf morphology and leaf chemical composition in three Quercus (Fagaceae) species along a rainfall gradient in NE Spain

Abstract Leaf features were examined in three Quercus species (Q. coccifera, Q. ilex and Q. faginea) along a steep rainfall gradient in NE Spain. The analyzed leaf traits were area, thickness, density, specific mass, leaf concentration of nitrogen, phosphorous, lignin, cellulose and hemicellulose, both on a dry weight basis (Nw, Pw, Lw, Cw, Hw) and on an area basis (Na, Pa, La, Ca, Ha). These traits were regressed against annual precipitation and correlated with each other, revealing different response patterns in the three species. Q. faginea, a deciduous tree, did not show any significant correlation with rainfall. In Q. coccifera, an evergreen shrub, Nw, Na, Lw, La and Ca increased with higher annual rainfall, while Hw decreased. In Q. ilex, an evergreen tree, leaf area, Pw and Lw increased with precipitation, whereas specific leaf mass, thickness and Ha showed the reverse response. Correlations between the leaf features revealed that specific mass variation in Q. faginea and Q. coccifera could be explained by changes in leaf density, while in Q. ilex specific leaf mass was correlated with thickness. Specific leaf mass in the three species appeared positively correlated with all the chemical components on a leaf area basis except with lignin in Q. ilex and with P in Q. ilex and Q. faginea. In these two tree species Pw showed a negative correlation with specific leaf mass. It is suggested that each species has a different mechanism to cope with water shortage which is to a great extent related to its structure as a whole, and to its habit.

Leaf morphology, leaf chemical composition and stem xylem characteristics in two Pistacia (Anacardiaceae) species along a climatic gradient

Summary Leaf and stem xylem features in Pistacia lentiscus (an evergreen shrub) and P. terebinthus (a deciduous shrub) were analysed along an Atlantic-Mediterranean gradient, which is characterised by a variation of rainfall and winter temperature. Leaf features were foliage area of 3-year-old shoots (FA), leaflet area (LA), specific mass (SLM), thickness (LTh), density (LD) and chemical composition on a dry weight basis (N, P, cellulose Cel, hemicellulose Hcel, and lignin Lig). Stem traits referred to xylem anatomy: mean vessel diameter of the 25 largest vessels (MxD), vessel element length (VEL), number of vessels per xylem cross section area unit (VD) and the ratio xylem/foliage surface of shoots (HV). Comparisons of traits have been made both at an interspecific and at an intraspecific level, this latter by analysing how these traits respond to variations of precipitation and winter temperature. P. terebinthus showed higher FA, LA, MxD, Nand Cel, but lower SLM, LTh, Hcel, VD and HV than P. lentiscus. Both species showed opposite responses of LTh to the reduction of mean minimum January temperature, decreasing in the former and increasing in the latter. In P. lentiscus VD increased and VEL decreased when winter temperature became colder, while YD decreased and N increased towards the arid part of the gradient. It is suggested that leaf habit plays an important role in determining the function of species and their response to the climatic gradient.

Trade-offs between phenology, relative growth rate, life form and seed mass among 22 Mediterranean woody species

Mediterranean woody plants exhibit a wide phenological diversity which cannot be explained just on the basis of climatic constraints. We assessed the role of relative growth rate (RGR), life form, seed and fruit mass as potential constraints of plant phenology. In a comparison of traits of 22 Mediterranean woody plant species, the duration of the primary shoot growing period decreased from climbers to shrubs and to trees. A hypothesised negative association between RGR and primary shoot growth duration did not emerge in our species set. The mechanism underlying phenological differences between plant life forms might relate to differences in the proportion of respiring to photosynthetic tissues, which decreases from climbers to trees. It is suggested that the degree of shoot preformation within the bud correlates with primary shoot growth duration, but not with RGR. Development of big fruits and seeds competes for carbon with vegetative growth. Indeed, species with bigger seeds and fruits exhibited shorter primary shoot growing periods, which tended to overlap with flower bud formation and flowering periods. We suggest that duration of primary shoot growth allow to short out the species between two extreme growth strategies: The conservative one would be characterised by a concentration of the primary shoot growth into a short period, free of frosts and droughts, and by a diversion of part of the current resources to assure next years growth. The opportunistic strategy, on the other extreme, would be defined by the allocation of resources to current growth whenever they are available, achieving longer growing periods at the expense of higher risk of tissue damage. These strategies should have been selected for in environments of predictable and unpredictable resource availability, respectively.

Effects of soil erosion on the floristic composition of plant communities on marl in northeast Spain

. This study explored the validity of three responses of vegetation to increased soil erosion: reduction of vegetation cover, number of species and reduced substitution of species. 201 releves, including edaphic and geomorphological data, were surveyed in the intensely eroded Eocene marls of the Prepyrenees (NE Spain). Changes in plant species’ presence in releves from different degradation stages were compared. The level of vegetation degradation was defined as the total phanerogam cover which, in the studied area, was correlated to the degree of soil erosion. The considered trends were validated. Reduction of phanerogam cover and species number were gradual from low to high-eroded areas. Vegetation degradation explained 48% of the species number variance. In the later stages of degradation a significant substitution of species was not observed, only a lower frequency of occurrence of several species that appeared in the whole set of releves. Through the process of degradation, 47% of species displayed significantly reduced frequencies as degradation increased, none showed a significant increase in frequency. It is concluded that there are no characteristic species in these plant communities that survive in the severely eroded marls. Among the few species that had increased in frequency, most only colonised favourable micro-environments.

The crystallization water of gypsum rocks is a relevant water source for plants

Some minerals, like gypsum, hold water in their crystalline structure. Although still unexplored, the use of such crystallization water by organisms would point to a completely new water source for life, critical under dry conditions. Here we use the fact that the isotopic composition of free water differs from gypsum crystallization water to show that plants can use crystallization water from the gypsum structure. The composition of the xylem sap of gypsum plants during summer shows closer values to gypsum crystallization water than to free soil water. Crystallization water represents a significant water source for organisms growing on gypsum, especially during summer, when it accounts for 70-90% of the water used by shallow-rooted plants. Given the widespread occurrence of gypsum in dry lands throughout the Earth and in Mars, these results may have important implications for arid land reclamation and exobiology.

Seasonal variability of dry matter content and its relationship with shoot growth and nonstructural carbohydrates

This study assesses how different phases of shoot growth underlie seasonal change in leaf and stem dry matter content (LDMC and SDMC, respectively) of 12 woody Mediterranean species. The relationship between LDMC and nonstructural carbohydrate (NSC) concentrations is also explored and the seasonal vs interspecies variability of LDMC compared. LDMC, SDMC and shoot elongation rate (SER) were measured on a monthly basis for a minimum of 12 months. Bud growth rate (BGR) and NSC concentrations were also assessed in several of the study species. LDMC and SDMC decreased during shoot elongation in spring and increased in summer, showing a significant negative correlation with SER, but were unrelated to BGR. Half of the species analysed showed a positive relationship between LDMC and NSC. Seasonal fluctuations of LDMC within species were higher than interspecies differences, and species ranking was significantly affected by the month of sampling, except during winter months. Seasonal changes in LDMC and SDMC are mainly related to shoot elongation phenology, and NSC sink-source relationships between old and growing organs can explain this relationship in some species. Owing to the high seasonal variability in LDMC, it is recommended that samples for comparative purposes should be collected as close to the winter as possible.

Does the Gradualness of Leaf Shedding Govern Nutrient Resorption from Senescing Leaves in Mediterranean Woody Plants

The resorption of nutrients from senescing leaves is a key component of the nutrient conservation strategy of plants. Despite its relevance, the regulation of the efficiency of this process is poorly understood. The aim of this work was to test the hypothesis that species that shed leaves gradually along the year are less efficient reabsorbing nutrients from senescing leaves than species that shed leaves in a short period. N-, P-, and K-resorption-efficiencies were measured in 11 Mediterranean species and regressed against an index of the gradualness of leaf shedding. Additionally, the bivariate relations among leaf nutrient content before senescence, nutrient content in senesced leaves, pool of nutrients reabsorbed during senescence, and nutrient resorption efficiency, were examined. K-resorption-efficiency was markedly lower in species with protracted leaf-shedding, in agreement with the initial hypothesis. This pattern was less significant for N- and P-resorption-efficiencies. When leaf nutrient content before senescence was high, the amount of nutrients reabsorbed and the amount of nutrients in senesced leaves were high. Consequently, nutrient resorption efficiency was unaffected by the leaf nutrient status before senescence. It is concluded that the leaf shedding pattern per se influences nutrient resorption in Mediterranean perennials, irrespective of additional environmental controls. Furthermore, it is suggested that plants differing in nutrient status do not exhibit different nutrient resorption efficiencies because the nutrient content of leaves before senescence affects the components of resorption efficiency in countervailing ways.

Comparison of floristic changes on vegetation affected by different levels of soil erosion in Miocene clays and Eocene marls from Northeast Spain

Increased soil erosion on Eocene marls from N Aragón (NE Spain) tends to reduce vegetation cover and plant species number, but little is known about its effect in the neighbouring Miocene clays. In this study, the vegetation of strongly eroded areas on Miocene clays was analysed in terms of erosion intensity and compared with Eocene marls. Relevés were carried out on uniform patches of vegetation affected by different levels of erosion. The degeneration of vegetation cover explained 34% of the variation in species number as opposed to 48% in marls, and a clear pattern of species replacement through the destruction of the vegetation cover was not observed. Approximately 25% of the species decreased significantly and 4% increased, as opposed to 47% and 0% in marls, respectively. Erosion on marls may be more severe (more disturbance) and less stressing for vegetation (more water availability) than on clays. The few species that colonized intermediate degeneration stages and highly eroded sites were more common in non-eroded areas in drier bioclimatic belts. Thus, the degeneration of vegetation by soil erosion favoured the establishment of xeric species. The ecological range of erosion-resistant species was not wider than non-resistant species. Overall, increased soil erosion selected for different plant species in marls than in clays.

An increase in canopy cover leads to masting in Quercusilex

Masting is the intermittent and synchronous production of large crops, but its relation to tree growth remains elusive despite the ecological relevance of mast seeding. The production of huge fruit crops has been linked to the accumulation and consumption of resources as nutrients and carbohydrates, but no conclusive assessment has supported this assumption. To evaluate if masting takes place once trees’ canopies reach maximum foliage, changes in canopy cover were measured in Quercus ilex susbp. ballota stands before and after a masting event using the normalized difference vegetation index (NDVI). The results on the whole underline that masting in Q. ilex occurred once maximum levels of NDVI and canopy cover were reached. After the masting event, NDVI dropped, leaf shedding increased and trees produced shorter shoots, narrower tree rings and fewer acorns than before the masting event. These findings support our contention that an increase in canopy cover precedes masting.