Regrowth capacity in relation to defence strategy in Stipa clarazii and Stipa trichotoma,native to semiarid Argentina

Abstract Plants can defend themselves against herbivores by either avoiding or tolerating herbivory. Since avoidance mechanisms divert resources to other than growth processes, it could be expected a lower regrowth capacity in species that avoid herbivory than in species that tolerate herbivory, particularly under competition for resources. We tested this hypothesis by quantifying the regrowth of a grazing‐avoidant (Stipa trichotoma Nees, synonymous Nasella trichotoma (Nees) Hackel ex Arechav.) and a grazing‐tolerant (Stipa clarazii Ball, synonymous Nasella clarazii (Ball) Barkworth) grass species native to semiarid Argentina, when growing either singly or in pairs (one individual of each species) under repeated defoliation in field conditions. Twenty pairs of plants were selected in an area codominated by both species. Plants were protected by a 60 cm‐diameter exclosure, in which the rest of the vegetation had been removed. The same procedure was followed with 20 single plants of each species. The same plants were clipped four times in 1996 and 1998 and five times in 1997. The response variable was the cumulative regrowth per plant at the end of each year. The regrowth was analysed for neutral detergent fibre and nitrogen content. Cumulative regrowth of S. clarazii was higher, similar, or lower than the cumulative regrowth of S. trichotoma in 1996, 1997, and 1998, respectively. Regrowth was reduced by interspecific competition, although there was no interaction between species and growing conditions (single or in pairs). Neutral detergent fibre content was consistently higher, whereas nitrogen content was consistently lower, in S. trichotoma than in S. clarazii. Collectively, our results did not support the hypothesis of higher regrowth capacity in the grazing‐tolerant species than in the grazing‐avoidant species. Further, our findings suggest herbivore tolerance is a previously unappreciated trait of S. trichotoma.     

The effect of copper on the growth of wood-rotting fungi and a blue-stain fungus

The effect of copper (II) ions on the growth of three brown-rot fungi, six white-rot fungi and one blue-stain fungus in solid medium was evaluated. The fungi were grown in malt extract agar with different concentrations of copper added, and the radial growth rate was determined. At the end of the incubation period, the mycelial biomass and the media pH were determined. The white-rot and blue-stain fungus grew up to 3 mM and 6 mM copper, respectively and the brown-rot fungi were the only ones that grew up to 10 mM, with higher growth rates than those shown by the other fungi. In general, the brown-rot fungi produced greater acidification in the culture media than the white-rot fungi and blue-stain fungus, and the acidification increased when the amount of copper was increased. The biomass production for the different species, in the absence or presence of copper, was not related to the radial growth rate, and the fungal species that produced the greatest biomass amounts did not correspond to those that presented the highest growth rates. The brown-rot fungi Wolfiporia cocos and Laetiporus sulfureus and blue-stain fungus Ophiostoma sp. demonstrated greater tolerance to high copper concentrations in solid medium than the white-rot fungi, determined as radial growth rate. On the other hand, the highest biomass producers in solid medium with copper added were the white-rot fungi Ganoderma australe and Trametes versicolor and the brown-rot fungus Gloeophyllum trabeum.     

Response of the grapevine rootstock Richter 110 to inoculation with native and selected arbuscular mycorrhizal fungi and growth performance in a replant vineyard

Two indigenous arbuscular mycorrhizal (AM) fungi from the Mediterranean wine growing area in the Northeast of Spain were isolated and classified as Glomus intraradices Schenck & Smith. Both native fungi were found to increase the growth of the vine rootstock 110 Richter under greenhouse conditions compared with G. intraradices (BEG 72) and a phosphorus (P) fertilization treatment. The effectivity of field inoculation of Cabernet Sauvignon plants grafted on Richter 110 with the former native fungi and with G. intraradices BEG 72 in a replant vineyard severely infested by the root-rot fungus Armillaria mellea (Vahl ex Fr.) Kummer was assessed. The native fungi were not effective at enhancing plant development, and only G. intraradices BEG 72, resulted in a positive response. Field inoculation with this selected fungus increased plant shoot dry weight at the end of the first growing season.     

Root growth response to defoliation in two Agropyron bunchgrasses: field observations with an improved root periscope

Summary Root growth responses to defoliation were observed in the field with an improved root periscope technique, which is described. The grazing tolerant, Eurasian bunchgrass, Agropyron desertorum, was compared with the very similar but grazing sensitive, North American bunchgrass, A. spicatum. Root length growth of clipped A. desertorum was about 50% of that of intact plants, while root elongation of clipped A. spicatum continued relatively unabated during ninety days of regrowth following severe defoliation. The reduced root growth in A. desertorum was correlated with the allocation of relatively more resources to aboveground regrowth, thus aiding reestablishment of the root: shoot balance. This balance was apparent in similar root mortality patterns of clipped and control A. desertorum plants in the season following defoliation. In clipped A. spicatum, however, root mortality increased in the winter following the season in which the clipping was done and continued into the subsequent growing season. Reduction of root growth following defoliation appears to be an effective mechanism to aid reestablishment of the photosynthetic canopy and the root: shoot balance. As such it contributes to both herbivory tolerance and maintenance of competitive ability.     

Herbivory,current velocity and algal regrowth: how does periphyton grow when the grazers have gone?

1. An experiment conducted in streamside channels was used to document the regrowth of grazed periphyton. Our objective was to determine the relative importance of current velocity, grazing duration, and grazer type in shaping the trajectory of algal and periphytic regrowth. 2. The grazing mayflies Baetis bicaudatus and Epeorus longimanus were used alone and in combination to create three grazing treatments at slow, medium and fast current (2–5, 15–20 and 30–40 cm s^?1, respectively). Duration treatments consisted of 2, 4, 6, 8, 10 days of grazing. Chlorophyll a and ash‐free dry mass (AFDM) accumulation on grazed tiles was measured (as periphytic AFDM and chlorophyll a, respectively) at 2, 4, 6, 8 and 10 days following the removal of grazers. 3. Chlorophyll a and AFDM was best predicted by interactions between current velocity, grazing duration and regrowth time. 4. The two grazer species did not differ in their effect on Chlorophyll a and AFDM during the period of periphytic regrowth that followed grazing. 5. Longer grazing duration reduced periphytic biomass, but also accelerated algal regrowth, and this growth enhancement was more pronounced at slower current velocities. 6. Data from this study suggest that herbivory can have important historical effects on periphytic accrual.     

Growth responses of arctic graminoids following grazing by captive lesser snow geese

The effects of grazing by captive goslings of the Lesser Snow Goose on coastal vegetation at La Pérouse By. Manitoba were investigated. Swards of Carex subspathacea, Festuca rubra and Calamagrostis deschampsioides were grazed once for different periods (0–180 min) and regrowth of vegetation determined, based on measurements of standing crop, net above-ground primary production (NAPP) and forage quality (leaf nitrogen content). The amounts of foliage removed from swards of Carex subspathacea increased with the length of the grazing period, but after 44 days of regrowth there were no significant differences in above-ground biomass between control and grazed plots. While the amount of foliage removed by goslings from swards of Festuca rubra increased with the length of the grazing period (except after 150 min of grazing), the increase in biomass following defoliation was similar among treatments. Goslings removed little biomass from swards of Calamagrostis deschampsioides, even when the opportunity for grazing was 180 min. No significant differences in standing-crop or NAPP between grazed and ungrazed plots were detected by the end of summer. Grazing had no significant effect on amounts of nitrogen in leaf tissue of all species, suggesting that faecal nitrogen was not rapidly incorporated into plant biomass within the growing season. Patterns of regrowth of these species are compared to that of Puccinellia phryganodes. An increase in goose numbers in recent years has led to birds foraging on less preferred species, such as Calamagrostis deschampsiodes and Festuca rubra. Their poor nutritional quality and a lack of a rapid growth response following defoliation may explain, in part, the decline in the weight of wild goslings recorded over the last decade.     

Grazing by Folsomia candida (Collembola) differentially affects mycelial morphology of the cord-forming basidiomycetes Hypholoma fasciculare, Phanerochaete velutina and Resinicium bicolor

Cord-forming basidiomycetes are important decomposers of dead wood in forest ecosystems but the impact of mycophagous soil invertebrates on their mycelia are little known. Here we investigate the effects of different grazing intensities of Collembola (Folsomia candida) on mycelial foraging patterns of the saprotrophic cord-forming basidiomycetes Hypholoma fasciculare, Phanerochaete velutina and Resinicium bicolor growing from beech (Fagus sylvatica) wood block inocula in dishes of non-sterile soil. Mycelial extension rate and hyphal coverage decreased with increased grazing intensity. R. bicolor was most affected, high grazing density resulting in only a few major cords remaining. Grazing of H. fasciculare often resulted in points of more rapid outgrowth as cords with a fanned margin. In grazed mycelia of P. velutina the main cords had fanned tips and lateral cords became branched. These results suggest that mycophagy by Collembola may hinder the growth of cord-forming fungi in woodlands, which might impact on the ability of these fungi to forage for and decompose dead organic material.     

A comparison of nematode-capturing efficiencies of fiveDactylella species at four temperatures

Conclusions The data and observations presented indicate that the factors controlling the nematode-capturing efficiency of predaceous fungi are complex. There seems to be little correlation between the ability to capture nematodes and the optimum growth rate of the capturing fungus, but there may be some relation between the motility of a nematode and the ease with which it may be captured. Since soil contains many fungi and nematodes competing for nutrients in fairly restricted spheres such as soil particles, bits of organic matter, or the rhizospheres of growing plants, the influence of a nematode-supporting fungus such asPenicillium digitatum on a predaceous fungus may be greater than the direct effect of some nematode upon the predaceous fungus or vice versa.     

A fungal root symbiont modifies plant resistance to an insect herbivore

Vesicular-arbuscular mycorrhizal (VAM) fungi are common root-colonizing symbionts that affect nutrient uptake by plants and can alter plant susceptibility to herbivores. I conducted a factorial experiment to test the hypotheses that colonization by VAM fungi (1) improves soybean (Glycine max) tolerance to grazing by folivorous Mexican bean beetle (Epilachna varivestis), and (2) indirectly affects herbivores by increasing host resistance. Soybean seedlings were inoculated with the VAM fungus Glomus etunicatum or VAM-free filtrate and fertilized with high-[P] or low-[P] fertilizer. After plants had grown for 7 weeks first-instar beetle larvae were placed on bagged leaves. Growth of soybean was little affected by grazing larvae, and no effects of treatments on tolerance of soybeans to herbivores were evident. Colonization by VAM fungus doubled the size of phosphorus-stressed plants but these plants were still half the size of plants given adequate phosphorus. High-[P] fertilizer increased levels of phosphorus and soluble carbohydrates, and decreased levels of soluble proteins in leaves of grazed plants. Colonization of grazed plants by VAM fungus had no significant effect on plant soluble carbohydrates, but increased concentration of phosphorus and decreased levels of proteins in phosphorus-stressed plants to concentrations similar to those of plants given adequate phosphorus. Mexican bean beetle mass at pupation, pupation rate, and survival to eclosion were greatest for beetles reared on phosphorus-stressed, VAM-colonized plants, refuting the hypothesis that VAM colonization improves host plant resistance. VAM colonization indirectly affected performance of Mexician bean beetle larvae by improving growth and nutrition of the host plant. Received: 28 February 1997 / Accepted: 23 June 1997     

Dieback of rural eucalypts: Response of foliar dietary quality and herbivory to defoliation

Rural dieback of Eucalyptus blakelyi trees growing on pastoral properties near Canberra is associated with chronic defoliation by insects. In order to test the effect of defoliation on subsequent herbivory, I artificially defoliated three healthy trees by clipping their terminal branchlets. The foliage that regrew on the clipped trees was nutritionally superior to the foliage it replaced, and was much more heavily damaged by grazing insects. There was a transient increase in the tannin content of the regrowth foliage, but this was apparently ineffective in defending it from subsequent herbivory. Compared with the foliage on nearby E. blakelyi trees that also produced major flushes of leaf growth during the same period, the regrowth on the clipped trees had enhanced dietary qualities and suffered more insect damage. Leaf age contributed to many of the differences in dietary quality, but when adjustments were made for the effects of leaf age the same trends remained. Five of the nearby trees were suffering from the chronic insect grazing associated with rural dieback, and the other five appeared healthy. The dietary quality of regrowth foliage on the clipped trees was qualitatively more similar to that of foliage on the dieback trees. Thus the chronic herbivory associated with rural dieback may be partly self-perpetuating, given this positive feedback between defoliation and dietary quality, and an apparent absence of other effective controls on insect populations.     

Allometric growth, disturbance regime, and dilemmas of controlling invasive plants: a model analysis

Disturbed communities are observed to be more susceptible to invasion by exotic species, suggesting that some attributes of the invaders may interact with disturbance regime to facilitate invasion success. Alternanthera philoxeroides, endemic to South America, is an amphibious clonal weed invading worldwide. It tends to colonize disturbed habitats such as riparian zones, floodplain wetlands and agricultural areas. We developed an analytical model to explore the interactive effects of two types of physical disturbances, shoot mowing and root fragmentation, on biomass production dynamics of A. philoxeroides. The model is based on two major biological assumptions: (1) allometric growth of root (belowground) vs. shoot (aboveground) biomass and (2) exponential regrowth of shoot biomass after mowing. The model analysis revealed that the interaction among allometric growth pattern, shoot mowing frequency and root fragmentation intensity might lead to diverse plant ‘fates’. For A. philoxeroides whose root allocation decreases with growing plant size, control by shoot mowing was faced with two dilemmas. (1) Shoot regrowth can be effectively suppressed by frequent mowing. However, frequent shoot mowing led to higher biomass allocation to thick storage roots, which enhanced the potential for faster future plant growth. (2) In the context of periodic shoot mowing, individual shoot biomass converged to a stable equilibrium value which was independent of the root fragmentation intensity. However, root fragmentation resulted in higher equilibrium population shoot biomass and higher frequency of shoot mowing required for effective control. In conclusion, the interaction between allometric growth and physical disturbances may partially account for the successful invasion of A. philoxeroides; improper mechanical control practices could function as disturbances and result in exacerbated invasion.     

Short-term regrowth responses of four steppe grassland species to grazing intensity, water and nitrogen in Inner Mongolia

Inner Mongolia steppe grasslands are widely used for livestock farming and the regrowth ability of grassland species is therefore strongly influenced not only by water and nutrient availability but also quite heavily by grazing. However, little is known on how grazing, water and nitrogen interactively affect the dominant C3 species (Leymus chinensis, Stipa grandis, Agropyron cristatum) and the C4 species (Cleistogenes squarrosa). Therefore in the 2007 and 2008 growing seasons, a field experiment was carried out to test the hypothesis that under different grazing intensities the dominant species show different short-term regrowth response to simultaneous variation in the availability of water and nitrogen. Single factor and interaction effects of the addition of water (rainfed vs. simulated wet-year) and nitrogen (0 or 25 kg N ha^?1) were analysed along a gradient of four grazing intensities (ungrazed, lightly, moderately and heavily grazed) after one month of grazing exclusion. Water and nitrogen addition affected short-term regrowth of all species in a similar way whereas species responded differently to grazing. Simulated wet-year water availability consistently resulted in higher standing biomass, relative growth rate and cellulase digestible organic matter yield. Supplementary nitrogen promoted standing biomass and crude protein concentration. The nutritive value of all species’ standing biomass showed a similar increase with more intensive grazing. However, heavy grazing led to a clear shift in the relative biomass of the species, i.e. mainly a promotion of the C4 grass, C. squarrosa. In contrast to our hypothesis, there were no differences among species in their response to water or nitrogen addition, whereas, heavy grazing induced the expected species-specific response. Our results suggest that heavy grazing rather than nitrogen or water determine short-term shifts in species composition of the investigated steppe ecosystem. Furthermore, differences in the species-specific growth response to grazing may increase the proportion of the C4 grass C. squarrosa in steppe communities, whereas higher availability of nitrogen and water may lead to higher forage biomass and nutritive value of all investigated species but in short-term cannot compensate for the grazing induced changes in species composition.     

Passive brigalow (Acacia harpophylla) woodland regeneration fails to recover floristic composition in an agricultural landscape

Regrowth (secondary) vegetation is increasingly seen as an important conservation alternative where there is inadequate cover of intact remnant, and more recently, the focus of potential biodiversity offsets. However, little is known of the functioning and dynamics of regrowth in comparison to remnant vegetation. This research tests whether the floristic composition and stand structure of brigalow (Acacia harpophylla) regrowth woodlands return to that of endangered brigalow remnant woodlands and the relationships of patterns in composition and structure to environmental drivers in the agricultural landscape of southern Queensland, Australia. Thirty‐eight sites were sampled for species composition (frequency), stand structure (foliage projected cover of strata) and environmental variables (spatial/patch characteristics), encompassing ungrazed and grazed old‐growth brigalow remnants and different aged brigalow regrowth (<20, 20–30, 30–40, >40 years since clearing). There was no difference in structure observed between grazed remnant and older regrowth (>40 years); however, ungrazed old‐growth remnants were structurally different to older regrowth. Ungrazed and grazed old‐growth remnants were compositionally different to all regrowth woodlands. The proportion of surrounding vegetation, land‐use type, patch grazing intensity and soil properties were highly correlated with patterns in composition and stand structure observed across the brigalow woodlands. While the stand structure of brigalow regrowth returns to that of remnant brigalow, the distinct floristic species composition of older regrowth may indicate a longer time period is needed for equivalence or a possible alternate stable state in these highly modified agricultural landscapes. To ensure the long‐term persistence of brigalow communities, further investigation of the development trajectory of brigalow regrowth is required; however, it is critical that intact brigalow remnant vegetation remains a priority for conservation strategy and policy.     

Tolerance of a perennial herb, <Emphasis Type="Italic">Pimpinella saxifraga</Emphasis>, to simulated flower herbivory and grazing: immediate repair of injury or postponed reproduction?

Perennial, polycarpic herbs can respond to herbivory either by (1) regrowth in the same season in order to compensate for lost reproductive structures or by (2) postponing reproduction until the following growing season. We tested these response patterns with the perennial umbellifer Pimpinella saxifraga by simulating flower herbivory and shoot grazing both in the field and in a common garden experiment. In the field, both simulated flower herbivory and grazing effectively suppressed current reproduction, whereas no statistically significant effects of previous-year treatments on growth or reproduction were found in the following year. In the common garden, in the first year the species fully compensated for simulated flower herbivory in vegetative parameters but seed set was reduced by 26%. After 2 years of flower removal, the plants overcompensated in shoot and root biomass by 47 and 46%, respectively, and compensated fully in reproductive performance. Simulated grazing resulted in 21% lower shoot biomass in the first season, but the root biomass was not affected. In the second season the root biomass increased by 43% as compared to the control plants. However, regrowth following simulated grazing resulted in a significant delay in flowering with the consequence that the seed yield of fertile plants was reduced by 55% as compared to the control plants. These results suggest that in resource-rich garden conditions P. saxifraga may immediately repair injuries caused by flower herbivory, but repairs more extensive shoot injury less successfully. Delayed phenology decreases the benefits of immediate repair. In resource-poor conditions, the benefits of regrowth can be negligible. Accordingly, in our field population, the plants postponed their reproduction until the following year in response to simulated grazing and frequently in response to flower removal. When the plants gain very little from regrowth, the costs of reproduction would select for postponed reproduction in response to injury.     

Tritrophic interactions in a soil community enhance decomposition rates

Microbivorous soil fauna can influence decomposition rates by regulating biomass and composition of the microbial community. The idea that predators at higher trophic levels regulate population densities of microbivorous fauna and thus indirectly increase microbial growth and activity has often been suggested but rarely examined in soil ecosystems. In this paper the effects of tritrophic interactions on decomposition processes in the soil are studied and expressed as soil respiration, hyphal lengths, cellulase and chitinase activities. The experiments were carried out in soil microcosms in a factorial design with three fungal species ( Alternaria alternata , Fusarium oxysporum , Trichoderma viride ), the fungivorous collembolan Folsomia fimetaria and the predatory mite Hypoaspis aculeifer . The respiration rate was significantly higher with three trophic levels than in those with two and lowest in those with only fungi present. This indicates that a low level of grazing stimulates microbial respiration more than a high level or no grazing at all. The effect was similar for all three fungal species but most pronounced in microcosms with the fungus A. alternata which was a preferred food source by the collembolans. Hyphal lengths were in all cases but with T. viride reduced in the presence of collembolans and predatory mites. T. viride had a slightly higher chitinase activity than the other fungi but increased numbers of trophic levels did not affect the enzymatic activities of any of the fungi.     

Colonization ofRetama raetam seeds by fungi and their significance in seed germination

Examination by scanning electron microscopy and incubation on potato-dextrose agar medium showed that dry seeds ofRetama raetam were externally free of fungi. When planted in sandy loam soil, the seeds become colonized with eleven soil-borne fungal species. The fungi were isolated on cellulose agar, pectin agar and lignin agar media.Aspergillus flavus, A. niger, A. fumigatus, Penicillium capsolatum andFusarium oxysporum had broad occurrence and were recovered on all the three media. The production of hydrolytic enzymes by the isolated fungi depends on the substrate and species.Penicillium capsolatum, P. spinulosum andA. niger had wide enzymatic amplitude and they were able to produce cellulolytic, pectolytic and lignolytic activities on corresponding substrates as well as on seed-coat-containing media. The lignolytic activities of the isolated species exceptChaetomium bostrychodes andTrichoderma viride were enhanced by applying the seed-coat materials as C- source rather than lignin. SoakingR. raetam seeds in culture filtrates of most of the fungi grown on seed-coat-supplemented media induced a pronounced and distinct stimulating effect on seed germination. The most effective filtrates were those ofP. capsolatum, P. spinulosum andSporotrichum pulverulentum.     

Interactions among ammonia fungi on MY agar medium with varying pH

Five early-phase ammonia fungi (EP fungi) – Amblyosporium botrytis, Ascobolus denudatus, Peziza moravecii, Pseudombrophila petrakii, Coprinopsis phlyctidospora, and Tephrocybe tesquorum, and one late-phase ammonia fungus (LP fungus), Hebeloma vinosophyllum – were co-cultured on malt extract-yeast extract agar media at pH 5.5, 7.0, 8.0, and 9.0. The co-cultures among the early-stage EP fungi Amblyosporium botrytis, Ascobolus denudatus, Peziza moravecii, and Pseudombrophila petrakii, generally did not inhibit or accelerate the reproductive structure formation of the opposed fungi. Among the EP fungi, Am. botrytis, As. denudatus, and Pe. moravecii intermingled with each other. The late-stage EP fungus T. tesquorum inhibited the growth of other EP fungi. Another late-stage EP fungus, C. phlyctidospora, showed ability to invade other EP fungi, but it did not deeply invade into the territories of early-stage EP fungi. The LP fungus H. vinosophyllum tended to accelerate basidioma formation of C. phlyctidospora at pH 5.5 and 9.0. H. vinosophyllum formed the highest numbers of basidomata at pH 5.5. These results show that successive occurrence of ammonia fungi is caused by the interspecific interactions among ammonia fungi as well as by the physiological characteristic of each fungus associated with conditions of its inhabiting soils, such as pH and nitrogen concentration.     

Filamentous fungi found in Atta sexdens rubropilosa colonies after treatment with different toxic bait formulations

Leaf‐cutting ants maintain a symbiotic relationship with basidiomycetous fungi cultivated as food. Here, we profiled the non‐symbiotic filamentous fungi in laboratory nests of Atta sexdens rubropilosa submitted to treatments with different toxic bait formulations (using the insecticide sulfluramide as the active ingredient). After treatment, several filamentous fungi were found in different nest compartments. Culture‐dependent techniques recovered a total of 93 fungal isolates comprising 10 genera, 11 species and four unidentified fungi. The genus Penicillium was prevalent in both control and insecticide treatments. Overall, the majority of fungal isolates obtained in this study are commonly found in soil. Escovopsis spp., the specialized parasite of the ant‐fungus mutualism was only recorded in the fungus gardens of nests submitted to the toxic treatments. Moreover, no correlation was found regarding the presence of fungi in the different nest compartments (chi‐square, P > 0.4182). This study reveals that Escovopsis spp. is not the only fungus to overgrow the fungus garden of debilitated nests, thus adding more evidence on the possible negative impacts of such alien fungi. As suggested by previous studies, fast‐growing filamentous fungi likely overgrow the fungus garden in such conditions.     

Comparative responses of the Savanna grasses Cenchrus ciliaris and Themeda triandra to defoliation

Summary Two perennial tussock grasses of savannas were compared in a glasshouse study to determine why they differed in their ability to withstand frequent, heavy grazing; Cenchrus ciliaris is tolerant and Themeda triandra is intolerant of heavy grazing. Frequent defoliation at weekly intervals for six weeks reduced shoot biomass production over a subsequent 42 day regrowth period compared with previously undefoliated plants (infrequent) in T. triandra, but not in C. ciliaris. Leaf area of T. triandra expanded rapidly following defoliation but high initial relative growth rates of shoots were not sustained after 14 days of regrowth because of reducing light utilising efficiency of leaves. Frequently defoliated plants were slower in rate of leaf area expansion and this was associated with reduced photosynthetic capacity of newly formed leaves, lower allocation of photosynthate to leaves but not lower tiller numbers. T. triandra appears well adapted to a regime where defoliation is sufficiently infrequent to allow carbon to be fixed to replace that used in initial leaf area expansion. In contrast, C. ciliaris is better adapted to frequent defoliation than is T. triandra, because horizontally orientated nodal tillers are produced below the defoliation level. This morphological adaptation resulted in a 10-fold higher leaf area remaining after defoliation compared with similarly defoliated T. triandra, which together with the maintenance of moderate levels of light utilising efficiency, contributed to the higher leaf area and shoot weight throughout the regrowth period.     

A physiological study of Saksenaea vasiformis Saksena

Summary The physiological conditions governing growth and sporulation ofSaksenaea vasiformis Saksena, a fungus with outstanding morphological features quite peculiar for Mucorales, were determined. Earlier studies made byTiwari (1955) on a strain of the same species had shown that this fungus is incapable of sporulating on any synthetic medium normally employed for growing fungi.The fungus had been found to have a high tolerance for very low and high pH values. It showed maximum growth at two pH values, one near neutral point, at pH 6, and another at high alkaline pH value, i.e., pH 11. Reason for this behaviour of this fungus has already been discussed. The most suitable temperature for the growth of the fungus was found to be between 30–35° C.Nearly all the carbon, nitrogen and sulphur sources which generally favour growth of fungi were found to support vegetative growth of this fungus as well. However, sporulation in this fungus had peculiar nutritional needs. Only some of the carbon sources, viz., arabinose, rhamnose, sorbose, galactose, lactose and citric acid which supported poor growth, were found to support good or excellent sporulation. But it may be stated that not all carbon sources supporting poor growth could induce sporulation of the organism. Also none of the nitrogen or sulphur sources could induce the fungus to sporulate in presence of glucose as carbon source.