Dry Mass Allocation Research Articles

A Comparison of the Impacts of Leaf‐ And Sap‐Feeding Insects on Growth and Allocation of Goldenrod

Many plants support both leaf— and sap—feeding insects, yet comparative studies of plant responses to different types of damage are rare. I compared the impacts of a leaf—chewing beetle (Trirhabda sp.), a xylem sap—feeding spittlebug (Philaenus spumarius), and a phloem sap—feeding aphid (Uroleucon caligatum) on growth of goldenrod (Solidago altissima). My goals were (1) to measure insect impacts on plant size as a function of herbivore loads, and (2) to determine the mechanisms by which insect feeding affects plant growth, using the techniques of plant growth analysis. Plants were grown outdoors in large pots, and insects were placed on them at a range of densities. A series of four whole—plant harvests was performed, with the final harvest occurring after 3 wk of insect feeding. Insect mass gain per plant was used as the basis for the comparison, since the insects differed greatly in size. Spittlebugs were the most damaging insect, beetles were intermediate, and no effects of aphid feeding were detected. After 3 wk of feeding, both spittlebugs and beetles reduced total leaf mass, total leaf area, and root mass, and the impact of the spittlebug was 5—6 times greater than that of the beetle. Spittlebug feeding also reduced the mass of the apical buds, stem mass, and the number of lateral stems, while beetle and aphid damage had no effect on these variables. Dry mass allocation to leaves, stems, and roots was generally not affected by insect feeding, resulting in smaller but proportionally similar plants by the end of the feeding period. Plant relative growth rates (dry mass increase per unit dry mass per day) were reduced by both spittlebugs and beetles but not aphids, and the impact of the spittlebug was more severe than that of the beetle. None of the insects affected net assimilation rates (dry mass increase per unit leaf area per day), indicating that the insects did not reduce plant growth by altering plant physiology. Instead, reductions in relative growth rates were explained by changes in plant morphology; feeding by both spittlebugs and beetles strongly reduced specific leaf area (leaf area/leaf mass). This reduction of leaf area relative to leaf mass was the mechanism by which both insects decreased plant relative growth rates. This result suggests an explanation for why simulated damage frequently fails to mimic damage by actual herbivores. When leaves are artificially removed by clipping there will be an immediate change in dry mass allocation patterns, but specific leaf area will not necessarily be affected.

Seasonal allocation of biomass and resources in the geophytic species Haemanthus pubescens subspecies pubescens in lowland coastal fynbos, South Africa

The seasonal biomass and resource allocation patterns of a perennial geophytic species, Haemanthus pubescens subspecies pubescens, were investigated. Four phenophases for the species were identified and the annual patterns of dry mass and resource allocation were identified from individuals sampled from natural populations. From the results, four general resource allocation patterns were identified: (1) mobile macronutrients (N, P and K) and Cu; (2) immobile macronutrients (Mg and Ca) and Mn; (3) soluble carbohydrates, starch, Zn and Fe; and (4) Na, all with their own distinctive allocation patterns. This study confirms distinct allocation patterns between the resources and biomass. Furthermore, it was found that environmental constraints contributed towards the differential seasonal allocation patterns of the resources and biomass. The development of an underground storage organ is regarded as an evolutionary mechanism to cope with soils of a low nutrient status, characteristic of the Cape fynbos, and as a strategy for the protection of dry matter and resources against seasonal periodic droughts and fires. Die seisoenale biomassa en reserwe toekenningspatrone van ’n meerjarige geofiet spesie, Haemanthus pubescens subspecies pubescens, is ondersoek. Vier fenofases is vir hierdie spesie geïdentifiseer en die jaarlikse patrone vir droë massa en reserwe toekennings is geïdentifiseer vanaf individue wat uit natuurlike populasies gemonster was. Uit die resultate is vier algemene reserwe toekenningspatrone geïdentifiseer vir: (1) mobiele makrovoedingselemente (N, P en K) sowel as Cu, (2) immobiele makrovoedingselemente (Mg en Ca) sowel as Mn, (3) oplosbare koolhidrate, stysel, Zn en Fe, en (4) natrium, almal met hul eie kenmerkende toekenningspatrone. Hierdie studie bevestig opvallende verskille tussen die toekenning van reserwes en die biomassa. Verder is dit ook gevind dat omgewingsbeperkings bydra tot die differensiële seisoenale toekenningspatrone van reserwes en biomassa. Om dié rede word die ontwikkeling van ’n ondergrondse stoororgaan beskou as ’n meganisme om die kenmerkende lae voedingstatusgronde van die Kaapse fynbos, te hanteer. Dit word ook as ’n strategie beskou om die minerale- en droë materiaal reserwes te beskerm teen seisoenale periodieke droogtes en veldbrande.

Comparative ecophysiology ofLarix kaempferi(Lamb.) Carr. andAbies veitchiiLindl. III. Analysis of factors determining the differences in root depth

AbstractA new method for analyzing growth is proposed to elucidate factors responsible for the differences in root depth ofLarix kaempferiandAbies veitchiiseedlings. Root depth (D) divides into three factors;urn:x-wiley:09123814:ere0073:equation:ere0073-math-0001where DW and L are dry weight of the root and total length of root elements, respectively. L/DW, specific root length, and D/L ratio represents the length of the root per unit root dry weight and the ratio of the depth to the total length of the root elements, respectively. Seedlings of the two species were grown from seeds and values of these three factors; root dry weight, specific root length and D/L ratio were periodically compared between the two species during growth. Irrespective of watering conditions, the factor that was almost entirely responsible for the differences in root depth between these two species was differences in specific root length, while there were virtually no differences in root dry weight or D/L ratio, indicating that allocation of dry mass to the root is equivalent and geometrical structure of the root system is similar. It is therefore concluded that the deeper roots which enableL. kaempferiseedlings to establish themselves during drought conditions on bare ground, unlikeA. veitchiiseedlings whose establishment is confined to the forest floor, are attained by their ability to extend their roots longer for a given amount of dry mass.

Whole-plant CO2 exchange of seedlings of two Pinus sylvestris L. provenances grown under simulated photoperiodic conditions of 50� and 60� N

Seedlings of Scots pine (Pinus sylvestris L.) from Russia (59°58′N) and Poland (53°34′N) were grown for 4 months in controlled environment chambers, simulating the photoperiod conditions of 50° and 60° N. The Russian population grown at 50° N showed earlier height growth cessation than the Polish population. Photoperiodic conditions of 60° N increased proportional allocation of dry mass to shoots and lowered allocation to roots in the Russian population, which also had greater allocation to roots than the Polish population in both treatments. Total non-structural carbohydrate concentrations in roots and secondary needles of both populations were significantly higher at the end of the 4 month growing season at 50° compared to 60° N. Net photosynthesis rates were similar for both provenances and both treatments. The rate of transpiration was higher and water-use efficiency lower for plants grown in long-day conditions of 60° N. The mean respiration rate of roots ranged between 30 and 36 nmol CO2 · g-1 dry mass · s-1 and was 2–4 times higher than values observed for needles. Root respiration rates were greater in the Polish than the Russian population. Despite this, the greater allocation to root dry mass of the Russian population resulted in greater root respiratory cost as a proportion of daily carbon gain. Overall, root respiration accounted for between 18 to 34% of the total daily net carbon assimilation of these populations. Root and total respiration as a proportion of net daily carbon assimilation were greater at 50° than 60°N. Mean net integrated CO2 gains were 2.2–2.5 mmol CO2 · day-1 for seedlings from Russia compared to 3 mmol CO2 · day-1 for Poland.

Growth of Actinorhizal Plants as Influenced by the Form of N with Special Reference to Myrica gale andAlnus incana

Growth of two actinorhizal species was studied in relation to the form of N supply in water culture. Non-nodulated bog myrtle (.Myrica gale) and grey alder (Alnus incana) were grown with NH4, NH4N03 or NO J (4 mol m-3 N). A nodulated series of bog myrtle was also cultivated in N-free medium. Relative growth rate (RGR), utilization rate of N, and shoot/root ratio were highest for the two species with the N completely supplied as NH4. In both species, nitrate was largely reduced in the roots and the presence of NOJ in combined-N supply always affected the RGR and N utilization rate negatively. Both N2 fixation and complete NO3 nutrition represented conditions of relative N-deficiency resulting in relatively low tissue-N concentrations and a greater allocation of dry mass to the roots. The physiological N status of nodulated M. gale plants was comparatively good, as indicated by a normal nodule weight ratio and a relatively high N2-fixing rate per unit nodule mass. However, whole-plant N2-fixing capacity remained relatively low in comparison with acquisition rates of N in combined-N plants. The anion charge from the nitrate reduction was largely directly excreted as an OH efflux. H + /N ratios generally agreed with the theory. In comparison with NH4 nutrition, carboxylate concentrations were higher in N2-fixing M. gale plants and the H+/N ratio in nodulated plants was less than unity below the value for ammonium plants as previously found for other actinorhizal species. Therefore, NH4 should be an energetically more attractive N source for actinorhizal plants than N2. The results agree with commonly accepted views on energetics of N uptake and assimilation in higher plants and support the concept of a basically similar physiological behaviour between non-legumes and legumes.

Effect of nodulation, nitrogen fixation and CO2 enrichment on the physiology, growth and dry mass allocation of seedlings of Alnus rubra Bong.

SUMMARYInoculated and uninoculated Alnus rubra Bong, seedlings were grown for 47 days in atmospheres containing ambient (350 μ1 CO2 1−1) and elevated (650 μl CO2 1−1) levels of CO2, with and without combined nitrogen (20 mg 1−1) supplied as ammonium nitrate. Five plants from each treatment were harvested 15, 30, and 47 days after exposure to CO2 treatments began. Evidence for the presence of a positive feedback loop between nitrogen fixation and photosynthesis was observed in nodulated plants growing at elevated CO2. These plants had greater whole‐plant photosynthesis and nitrogenase activity, leaf area and nitrogen content, as well as nodule and plant dry mass, relative to nodulated plants grown at ambient CO2 and non‐nodulated plants grown at both CO2 levels. This feedback may be an important way in which the potential carbon drain of nitrogen fixation on the host plant could be compensated; increased nitrogen availability resulting in stimulated leaf area growth and whole‐plant photosynthesis. The relative amount of dry mass allocated below ground decreased for all seedlings over time, and the amount allocated above ground increased. This shift in allocation occurred slowly and at a constant rate in non‐nodulated plants and more rapidly and abruptly when plants were nodulated. The proportion of dry mass allocated below ground was consistently greater in non‐nodulated plants. Dry mass allocation to the stem was increased when combined nitrogen was applied and was greatest in nodulated plants grown at high CO2. Dry mass partitioning among other organs was not directly affected by nodulation, CO2 enrichment, or other treatment interactions.

Effects of Flooding and Root Competition on Growth of Shaded Bottomland Hardwood Seedlings

Effects of Flooding and Root Competition on Growth of Shaded Bottomland Hardwood Seedlings

Seasonal allocation of dry mass and nitrogen in a fynbos endemic Restionaceae species Thamnochortus punctatus Pill.

The annual growth pattern of male plants of the endemic, dioecious fynbos species, Thamnochortus punctatus, revealed sequential growth of the various below-and above-ground organs. Root and rhizome development were favoured in the wet winter months while culm elongation occurred in the warmer but drier spring to summer period. The reproductive phase of development followed in the hot dry summer and autumn. The asynchronous pattern of growth is suggested to enable the plant to maximize utilization of scarce resources within the confines of the environmental controls determined by the mediterranean-climate. Maximum root and rhizome activity in the rainy season enabled the plant to absorb and store nitrogen in mature culms for later above ground organ development. As the absorption of nitrogen from senscing material is essential for this pattern of organ development to assist in alleviating nutrient scarcity the high degree of nitrogen reabsorption, 35 to 70% for branches and culms respectively, shows the potential importance of asynchronous organ growth in overcoming nitrogen limitation of plant growth. Comparisons of dry mass and nitrogen allocation patterns indicate that developmental strategies employed by evergreen, perennial plants in climatically and edaphically constrained environments cannot be deduced from biomass allocation patterns alone as they do not appear to reflect strategies evolved to overcome nutrient limitation.