Trunk Growth Rate Research Articles

Evaluation of grapevine water status from trunk diameter variations

We evaluated the usefulness of short-term trunk diameter variations (TDV) as water stress indicator in field-grown grapevines cv. Tempranillo. Two indices were calculated from TDV, maximum daily trunk shrinkage (MDS), and trunk growth rate (TGR). The seasonal evolution of both indicators was compared with occasional determinations of pre-dawn leaf water potential and stem water potential, measured at early morning (Ψ s em ) and at midday (Ψ s md ) in irrigated and non-irrigated vines. In the second season, the effect of crop load on the vine water status indicators was also studied. Crop load did not affect either the vine water relations or the TDV. All water potential determinations had much lower variability and were more sensitive than both MDS and TGR to water restrictions. The ability of both indices to detect plant water stress varied largely depending upon the phenological period. In fact, MDS and TGR were only able to detect vine water stress during a short period of time before veraison. During this period, TGR was linearly related to both Ψ s em and Ψ s md , while for MDS a curvilinear, quadratic equation, better described the relationship with plant water status. After veraison no apparent relationship existed between plant water status and MDS or TGR. Hence, our results question the practical use of both MDS and TGR as variables to automate irrigation scheduling for grapevine.

Crop load affects maximum daily trunk shrinkage of plum trees

We studied the effects of low fruit load (3-4 fruits cm(-2) of trunk cross-sectional area (TCSA), and high fruit load (6-7 fruits cm(-2) TCSA) on maximum daily trunk shrinkage (MDS) and trunk growth rates (TGR) over two seasons in plum (Prunus salicina Lindell) trees receiving full irrigation or deficit irrigation. Seasonal changes in MDS and TGR were compared with those in midday stem water potential (Psi(s)) and leaf stomatal conductance (g (s)). Crop load increased g (s) in fully irrigated trees approaching harvest. Although crop load did not affect plant water status in either watering regime, there were considerable differences in both MDS and TGR as a function of crop load. Compared with low-cropping [corrected] trees, MDS was 34% higher and TGR was 48% lower in high-cropping [corrected] trees. The differential responses of MDS and Psi(s) to crop load were a consequence of a higher MDS for a given Psi(s) in the high-cropping trees compared with the low-cropping trees. There was a linear increase in MDS with crop load, with a slope of 15.2 microm MPa(-1) per unit increment of crop load. In the fully irrigated trees, day-to-day variations in MDS were related to evaporative demand; however, the slope of the relationship between MDS and evaporative demand increased with crop load, indicating that different reference equations must be used to adjust for tree crop load when using MDS to determine plant water status and irrigation requirements.

Evaluation of plant-based water status indicators in mature apple trees under field conditions

The performance of different indicators of plant water status as a tool for irrigation management was evaluated in mature field grown ‘Golden Delicious’ apple trees during the late summer of 1998. Control (C) and stress (S) treatments were studied. In the C treatment trees were irrigated daily at 100% ETc whereas in the S treatment water was withheld during 31 days (DOY’s 236–266). Predawn water potential (Ψpd) and midday stem water potential (Ψstem) were measured several times a week during the experimental period. Three daily measurements of stomatal conductance (gs) and stem water potential were made during five consecutive days in mid-September. Trunk diameter changes (TDC) were recorded by LVDT sensors, and from these measurements, maximum daily shrinkage (MDS), daily growth (DG), and cumulative growth (CG) were calculated. Midday Ψstem showed the best ratio between the response to moderate water stress and tree variability (“signal/noise” ratio) among the indicators studied here, followed closely by Ψpd. On the other hand, the poorest water status indicator was gs. Due to the low trunk growth rate of the trees, and its high variability, DG and CG were not adequate indicators. MDS showed a lower sensitivity to water stress and a higher variability (CV = 0.19) than midday Ψstem (CV = 0.08) and Ψpd (CV = 0.10). However, MDS correlated well with ET0 and with midday Ψstem (R2 = 0.79) thus, making this parameter an interesting and promising tool for irrigation management in apple orchards. More research needs to be done in order to define reference values for MDS and plant water potential indicators, in relation to evaporative conditions and in different phenological periods, and to quantify the relationship between water status indicators values and apple tree yield and fruit quality.

Seasonal, daily and diurnal variations in the stable carbon isotope composition of carbon dioxide respired by tree trunks in a deciduous oak forest

The stable C isotope composition (delta13C) of CO2 respired by trunks was examined in a mature temperate deciduous oak forest (Quercus petraea). Month-to-month, day-to-day and diurnal, measurements were made to determine the range of variations at different temporal scales. Trunk growth and respiration rates were assessed. Phloem tissue was sampled and was analysed for total organic matter and soluble sugar 13C composition. The CO2 respired by trunk was always enriched in 13C relative to the total organic matter, sometimes by as much as 5 per thousand. The delta13C of respired CO2 exhibited a large seasonal variation (3.3 per thousand), with a relative maximum at the beginning of the growth period. The lowest values occurred in summer when the respiration rates were maximal. After the cessation of radial trunk growth, the respired CO2 delta13C values showed a progressive increase, which was linked to a parallel increase in soluble sugar content in the phloem tissue (R=0.95; P<0.01). At the same time, the respiration rates declined. This limited use of the substrate pool might allow the discrimination during respiration to be more strongly expressed. The late-season increase in CO2 delta13C might also be linked to a shift from recently assimilated C to reserves. At the seasonal scale, CO2 delta13C was negatively correlated with air temperature (R=-0.80; P<0.01). The diurnal variation sometimes reached 3 per thousand, but the range and the pattern depended on the period within the growing season. Contrary to expectations, diurnal variations were maximal in winter and spring when the leaves were missing or not totally functional. By contrast to the seasonal scale, these diurnal variations were not related to air temperature or sugar content. Our study shows that seasonal and diurnal variations of respired 13C exhibited a similar large range but were probably explained by different mechanisms.

Performance of various water stress indicators for prediction of fruit size response to deficit irrigation in plum

The performance of several continuous and discontinuous measurements of soil and plant water status was studied in a drip-irrigation experiment on plum ( Prunus salicina Lindl. ‘Black Gold’) where different levels of water restriction during the fruit growth period were imposed, and compared to a more irrigated (control treatment) over 2 years. Soil matric potential ( Ψ m) was measured with granular matrix sensors (Watermark ®) and short period variations of trunk diameter (TDV) with lineal variable differential transformer sensors. From TDV measurements, maximum daily shrinkage (MDS) and trunk growth rate (TGR) were calculated. Besides, predawn leaf water potential ( Ψ pd), midday stem water potential ( Ψ stem), and midday stomatal conductance (gs) were measured along both seasons. The seasonal variation of all indicators showed that, under mild water restrictions that reduced fruit weight and yield, Ψ m and TGR did not gave a clear indication of a decrease in soil or plant water status. Instead, the evolution of the rest of indicators was in reasonable agreement with timing and severity of the water deficit applied. The degree of correlation between the various water status indicators and fruit weight at harvest was as follows: ( Ψ stem ≅ Ψ pd ≅ gs > MDS > TGR > Ψ m), but gs was much more variable than Ψ pd and Ψ stem. Based on these results we conclude that, although MDS, TGR and Ψ m provide continuous measurement of plant and soil water status, both Ψ pd and Ψ stem should be preferable as water stress indicators in plum.

Comparison of changes in stem diameter and water potential values for detecting water stress in young almond trees

Trunk diameter fluctuations (TDF) and the leaf water relation parameters, predawn and midday leaf water potential ( Ψ pd and Ψ md), midday stem water potential ( Ψ st) and midday leaf conductance ( g l) were compared for use in detecting water stress and for helping with irrigation management in young almond trees. TDF were monitored throughout 2002 in three irrigation treatments: T 1 (control), irrigated at 120% of crop evapotranspiration (ETc), T 2, at 60% ETc for the whole year and T 3, irrigated at 100% ETc except between 3 June and 15 September, when 40% ETc was supplied. The annual reference crop evapotranspiration and rainfall during the experiment were 1375 and 320 mm, respectively, while the amount of water applied in the treatments was 3165, 1525 and 1430 m 3 ha −1 year −1 for T 1, T 2 and T 3. These irrigation treatments had Ψ st that varied over the season from around −0.65 to −1.0; −0.9 to −1.3 and −0.7 to −1.5 MPa, respectively. Two parameters were obtained from the TDF measurements: (i) maximum daily trunk shrinkage (MDS) and (ii) trunk growth rate (TGR). The MDS values were influenced by the evaporative demand and varied greatly between trees (CV around 10–35%). Although all the water status indicators showed a response to the water supply, the greatest changes were observed in Ψ pd, Ψ st and TGR. The results obtained indicate that MDS and TGR were sensitive to water stress and that TGR is the most useful parameter for quantifying water deficit intensity and duration, its behaviour being very similar to that of Ψ pd and Ψ st. It is concluded that TGR is useful as an indicator of stress and could serve for making irrigation decisions in young almond trees.

ESTABLISHING REFERENCE VALUES OF TRUNK DIAMETER FLUCTUATIONS AND STEM WATER POTENTIAL FOR IRRIGATION SCHEDULING OF OLIVE TREES

Trunk diameter fluctuations (TDF) and stem water potential (SWP) were recorded in well-irrigated olive trees with the aim of establishing reference values of both indicators for irrigation scheduling. The measurements were performed in a mature (18 years) and a young olive orchard (3 years) during 4 years. Two different indicators derived from TDF: maximum daily shrinkage (MDS) and trunk growth rate (TGR) were evaluated. The annual relationship between MDS and vapour pressure deficit (VPD) was hysteretic, probably caused by the presence of fruit as no hysteresis was detected in ‘off’ trees. All data pooled gave an equation of MDS=0.09+0.19VPD (R 2 =0.60). When only data until mid-August in mature “on” trees was used, the fit was improved (R 2 =0.71; MDS=0.05+0.22VPD). Young trees had a slightly different relationship with a steeper slope; MDS=-0.18+0.27VPD (R 2 =0.80). The relationships between the SWP values and VPD were not as good as with MDS (R 2 around 0.3), and the regression slope was steeper in ‘on’ than in ‘off’ trees. TGR in the young orchard had two maxima in the year; the first at mid-Spring (0.2 mm day -1 ) and the second at the end of the summer (0.15 mm day -1 ). In the mature orchard, TGR had a single maximum value, at the end of summer for ‘off’ trees, and in spring for ‘on’ trees.

Interpreting trunk diameter changes in young lemon trees under deficit irrigation

Measurements obtained by the continuous monitoring of sap flow and parameters derived from trunk diameter fluctuations were compared with discrete measurements of conventional plant water status indicators in potted young lemon trees ( Citrus limon (l.) Burm. fil, cv. Verna) grafted on sour orange ( C. aurantium L.) rootstock submitted to high frequency deficit irrigation. The first detectable response to the deficit irrigation was a marked increase in maximum daily trunk diameter shrinkage (MDS) followed by a decrease in sap flow (SF), predawn leaf water potential and leaf conductance values. Daily maximum (MXTD) and minimum (MNTD) trunk diameters were directly influenced by the plant water supply from the soil. When the water stress increased in severity and the trunk growth rate increased, the MDS values in treated plants decreased to reach values similar to those of control plants. Thus, during the first days of deficit irrigation, when trunk growth was very low, MDS and SF served as the best plant water status indicators. Further, when water stress was more pronounced and trunk growth was greater, MNTD, MXTD and SF were the most reliable indicators.

Continuous measurement of plant and soil water status for irrigation scheduling in plum

The usefulness of continuous measurement of soil and plant water status for automated irrigation scheduling was studied in a drip-irrigation experiment on plum (Prunus salicina Black Gold). Two levels of water restriction were imposed at different phenological periods (from pit-hardening to harvest, post-harvest) and compared with a well irrigated control treatment. Soil matrix water potential (ψsoil) was measured with granular matrix sensors (Watermark); and short-period trunk diameter variation (TDV) was measured with linear variable displacement transformers. The Watermark sensor readings were in reasonable agreement with the irrigation regime and showed a good indication of plant water status across the season (r2=0.62), although they were a better predictor of stem water potential (ψstem) in the dry range of ψsoil. Nonetheless, the most important drawback in their use was the high variability of readings (typical CV of 35–50%). From TDV measurements, maximum daily shrinkage (MDS) and trunk growth rate (TGR) were calculated. Their performance was also compared with ψstem, which had the lowest variability (CV of 7%). During most of the fruit growth period, when TGR was minimum, MDS was higher in the less-irrigated treatment than in the control and correlated well (r2=0.89) with ψstem. However, after harvest, when TGR was higher, this correlation decreased as the season progressed (r2=0.73–0.52), as did the slope between MDS and ψstem, suggesting tissue elasticity changes. Later in the season, TGR was better related to plant water status. These observations indicate some of the difficulties in obtaining reference values useful for irrigation scheduling based exclusively on plant water status measurements.

Effects of Nutrient Limitation on Aboveground Carbon Dynamics during Tropical Dry Forest Regeneration in Yucat�n, Mexico

Tree growth (as diameter increment), litterfall production, and litter biomass were studied in two secondary tropical dry forests of the Yucatan Peninsula under four treatments of nutrient addition. The study’s objective was to assess how variations in the nutrient supply affect aboveground net primary production and carbon (C) accumulation on the floor of two forests in different stages of regeneration. The study included an area of young forest (10 years old) with phosphorus (P)-poor soils and an area of old forest (around 60 years old) where soil P was comparatively less limiting. Four replicate plots (12 × 12 m) at each forest were either left intact (controls) or fertilized with nitrogen (N), P, or N plus P during 3 consecutive years. After 3 years of fertilization, relaxation of the constraints on nutrient limitation resulted in increased trunk growth rates at both the young and old forests. This effect was more pronounced with the addition of P or N plus P (trunk growth doubled with respect to controls), whereas N addition increased tree growth by 60% in comparison to trees in plots without nutrient supplements. In both forests, there were no significant differences in litterfall production among treatments during the first 2 years after fertilization. In the 3rd year of nutrient addition, litterfall production was significantly higher in plots fertilized with N plus P compared to control plots at both forest sites; however, changes in litterfall were not accompanied by litter accumulation in the floor of the two forests. The results of this study support the hypothesis that there is nutrient limitation during tropical dry forest regeneration. They further show that it may be maintained in the long term during secondary succession.

Plant indicators for scheduling irrigation of young olive trees

The sensitivity of several water status indicators was determined in irrigated young olive trees subjected to two drought periods at Cordoba, Spain. Trunk diameter fluctuations (TDF) were monitored continuously and stem water potential (ψ), leaf photosynthesis (P n) and conductance (g l) were measured periodically on trees where irrigation was interrupted or which were fully irrigated. During the first period of water deprivation in late spring, only some of the TDF-derived parameters were able to detect significant differences caused by water deficits, while there were no differences in stem ψ, P n and g l. All water stress indicators responded during the second drought period in midsummer. However, differences in maximum trunk diameter were detected several days before significant stem ψ differences of about 0.2 MPa were established between treatments. Stem ψ differences declined further to 0.6 MPa before differences in leaf P n and g l became significant. Of all TDF-derived indices, trunk growth rate was the most sensitive to water deficits while treatment differences in maximum daily shrinkage were insignificant in the young trees. It is concluded that continuous monitoring of trunk diameter provides the most sensitive indicator for accurate, automated irrigation scheduling of young olive trees under intensive production.

Phenology and drought affects the relationship between daily trunk shrinkage and midday stem water potential of peach trees

SummaryThe relationship between maximum daily shrinkage in trunks (MDS), daily trunk growth (DTG), predawn water potential (Ψpd) and midday stem water potential (Ψstem) were studied in an irrigation experiment in peach trees. Control trees were irrigated to replace evapotranspiration, with trees receiving regulated deficit irrigation (RDI) watered at 35% of this rate during Stage II of fruit development and after harvest. The RDI trees were watered as controls during Stage III of fruit development. Minimum (Ψpd and Ψstem fell to –0.6.MPa and –1.2 MPa, respectively in RDI plots compared with –0.2 and –0.6 MPa in the controls. Trunk growth was less in the RDI plots than in the controls during drought. In contrast, MDS was higher when deficit irrigation was applied in the RDI trees. When site differences were considered the correlation between (Ψpd and accumulated trunk growth over an ample period was loose, while maximum daily shrinkage and midday stem water potential remarkably improved such a correlation. However, pooling all available data, the correlation between Ψstem and MDS was very poor (R2=0.44) and it substantially improved only when using data from specific phenological periods (i.e. R2=0.75). A seasonal drift in MDS values was observed and it was related to the seasonal changes in trunk growth rates, (i.e. highest shrinkage was found when growth rates were lowest). We concluded that phenology in combination with drought reduce the reliability of the water status information obtained from MDS.

Irrigation scheduling protocols using continuously recorded trunk diameter measurements

Theoretical and experimental aspects of developing irrigation scheduling strategies using continuous measurements of trunk diameter are presented. The behavior of parameters derived from trunk diameter measurements (TDM), including maximum daily trunk shrinkage (MDS), maximum daily trunk diameter (MXTD), and minimum daily trunk diameter (MNTD) is evaluated for both rapidly growing peach [Prunus persica (L.) Batsch, cv. September Snow] and mature almond [Prunus dulcis (Mill.) Webb cv. Price] trees subjected to mild deficit irrigation. Stem water potential (SWP) and MDS were highly correlated in the mature almond trees but a poor relationship was found in the rapidly growing peach trees. Conversely, daily changes in MXTD and MNTD correlated well with SWP in the fast growing trees. While there was relatively high variability ("noise") in the MDS measurements (CV 15.8%), the greater changes in the magnitude of the MDS ("signal") resulted in a significantly higher signal:noise ratio than found with the SWP measurements. In addition to soil water and trunk growth rate, MDS patterns were influenced by irrigation frequency and evaporative demand. Based on the experimental results, protocols for utilizing the trunk diameter-derived indicators for scheduling irrigations are presented for three cases: (1) mature trees under low frequency irrigation, (2) mature trees under high frequency irrigation, and (3) young trees under high frequency irrigation. The scheduling protocols provide guidelines that address both under- and over-irrigation and are predicated on the sensitivity of TDM to very mild plant water deficits. The necessity for and approaches to developing reference (baseline) and threshold values derived from TDM are emphasized. We conclude that protocols using TDM for precise irrigation scheduling hold promise as an additional tool for progressive growers who want to link irrigation management to an automated, electronic, plant-based stress indicator.

EFFECTS OF POLLARDING AND WATHER ON THE INCREMENTAL TRUNK GROWTH OF COMMON LIME (TILIA X EUROPAEA) IN AN URBAN CONTEXT

Summary Core were taken from the trunks of thirty-five pollarded and thirty-five unpollarded lime trees (Tilia x europaea) in Kidderminster, Worcestershire, and annual growth rings were measured. The act of pollarding led to an initial growth spurt then, for a few years, a relative decline in trunk growth rate. Data suggest that weather, especially temperature and rainfall regimes of the preceding seasons, together with a range of site effects, including inter-tree spacing and soil, had a greater impact on annual trunk growth than pollarding. It was difficult to ascertain any convincing environmental relationships with non pollarded trees.

Growth of Trees on the Virginia Tech Campus in Response to Various Factors

Soil stresses allegedly repress tree health, growth, and longevity. Such stresses commonly occur on college campuses where soil compaction can result from pedestrian and vehicular traffic. Trees on campuses, as their forest counterparts, also sustain damage from storms and biotic stress agents. We monitored an expression of stress on selected trees on sites judged to be stressful or nonstressful (control) on the Virginia Tech campus. We measured dbh (diameter at breast height) of 9 species and crown diameter of 8 species, from 1993 to 1995. Trunk growth rates differed significantly among species. Five major factors influenced growth of trees: ice damage, percentage of paved area beneath the crown, heart rot, chlorosis, and Dutch elm disease. Almost half (49%) of trees were injured physically or manifested disease or rot. We also compared growth rates of trees in 2 groups classified by percentage of paved area beneath the crown, viz. low stress versus presumed stressed sites. Annual rates of trunk growth of campus trees were higher than comparative growth rates of the same species in forests. This was the combined result of several factors, including the fact that open-grown trees, lacking competition in a forest, grow faster. Based on our results, we cannot state conclusively that site stress suppressed growth of trees on campus. Health and longevity variables were not monitored.

Short-term recombinant human growth hormone treatment increases growth rate in achondroplasia.

To investigate the effect of recombinant hGH treatment on the growth rate and proportion of individuals with achondroplasia and hypochondroplasia, we studied 15 individuals with these common skeletal dysplasias. The study lasted 24 months and included 6 months of observation, 12 months of hGH therapy (0.04 mg/kg.day), and 6 months of posttreatment growth rate determination. In achondroplasia, the mean growth rate during the hGH treatment (5.3 +/- 1.6 cm) was significantly increased compared with that during the pretreatment (4.0 +/- 1.0 cm.yr, P < 0.01)) and posttreatment periods (3.1 +/- 1.3 cm; P < 0.001). In the 4 children with hypochondroplasia, the growth rate during hGH treatment was 7.0 +/- 2.4 cm/yr and 4.9 +/- 1.5 cm/yr during the pre- and posttreatment periods, respectively. In achondroplasia, there was a significant increase in growth rate of only the lower segment (from 1.1 +/- 1.6 cm/yr to 3 +/- 1.2 cm/yr, P < 0.02). There was no significant acceleration in the growth of the upper segment and of the scanogram measurements of the long bones. No untoward effects were noted. Recombinant hGH increases short-term growth velocity in children with achondroplasia/hypochondroplasia. Unexpectedly, this treatment does not seem to have a lesser effect on limbs than on trunk growth rate and, therefore, during 1 yr of treatment, does not increase body disproportion.

Production Method Affects Tree Establishment in the Landscape

Abstract Trunk growth rates one year after transplanting 5 cm (2 in) caliper laurel oak (Quercus laurifolia Michx.) from above-ground plastic containers, from in-ground fabric containers or from the field (B&amp;B) matched or exceeded growth rates before transplanting. Growth rates for all three treatments were similar seven months after transplanting. Shoots on field-grown trees grew more in the first year after transplanting than those from fabric or plastic containers. Roots removed at the time of digging were completely replaced on field and fabric container trees six months after transplanting. One year after transplanting, roots occupied the same soil volume as just prior to transplanting. Trees from plastic containers regenerated roots slower than B&amp;B trees or those from fabric containers. When irrigation frequency was reduced 14 weeks after transplanting (WAT), trees from plastic containers were water stressed more (had more negative xylem potential) than B&amp;B or fabric container trees. Growth rates of East Palatka holly (Ilex × attenuata Ashe. ‘East Palatka’) responded similarly to laurel oak; however hollies took longer to establish roots into landscape soil and took longer for the trunk growth rate to match that on trees prior to transplanting.

Water Relations of Field-grown Quercus virginiana Mill. from Preharvest through Containerization and 1 Year into a Landscape

Large (≈5 m high) Quercus virginiana Mill. (live oak) trees produced in 0.64-m-diameter in-ground fabric containers were root pruned or not root pruned inside containers before harvest. Harvested trees were grown in two sizes of polyethylene containers for 10 months, then transplanted into a landscape. Water potential (ψT) of small branches (&lt;4 mm in diameter) was measured diurnally during containerization and for 1 year in the landscape. Root pruning had no influence on postharvest survival. Neither root pruning nor container size affected tree water status during containerization or in the landscape. All surviving trees recovered from transplant shock following harvest after 16 weeks in a container, independent of treatment. In the landscape, 35 weeks of daily irrigation were required before dusk ψT declined to within 0.1 MPa of predawn values, a result indicating alleviation of transplant shock. Trunk growth rate during containerization was highest in larger containers. However, in the landscape, root pruning and small containers were associated with higher trunk growth rate. Tree water status during containerization and in the landscape is discussed.

Growth rate of a deep-sea coral using 210Pb and other isotopes

A deep-sea coral was studied to determine its growth rate and to reconstruct time histories of isotope distributions in the deep ocean. The specimen was collected at a depth of 600 m off Little Bahama Banks using the Deep Submergence Vehicle (DSV) Alvin. The growth rate of the calcitic coral trunk was determined using excess 210Pb measured in concentric bands. Excess 210Pb was found in the outer half of the coral's radius, and a growth rate of 0.11 ± 0.02 mm/a is calculated. Assuming a constant growth rate during formation of the entire trunk, an age of 180 ± 40 a is estimated for the coral. The decrease observed in radiocarbon activities measured on the same bands ( Griffin and Druffel, 1989) concurred with the growth rate estimated from excess 210Pb activity. 239,240pu activities measured by mass spectrometry were also detected in the outer two bands of the coral, as expected from the 210Pb chronology. Stable oxygen and carbon isotopes measured in samples collected by a variety of techniques are positively correlated. This is evidence of a variable kinetic isotope effect most likely caused by variations in the skeletal growth rate. Long-lived corals such as this specimen have the potential for serving as integrators of seawater chemistry in the deep-sea over several century timescales.

HETEROZYGOSITY AND DEVELOPMENTAL STABILITY UNDER INBREEDING AND CROSSBREEDING IN PINUS ATTENUATA.

The relationship between stability of annual trunk growth and heterozygosity at 24 polymorphic isozyme loci was studied in 10-year-old trees of knobcone pine (Pinus attenuata Lemm.) that were the products of contrasting systems of mating, self-, and interpopulation cross-pollination. Heterozygosity and variability of trunk growth were strongly related only when inbreds and crossbreds were compared; the crossbreds showed greater residual variability on an absolute scale, and greater responsiveness to climate on both absolute and relative scales. Within the inbreds there was no evidence of a relationship between heterozygosity and variability. Within the crossbreds, only one trait, a measure of relative trunk growth rate, showed a relationship with heterozygosity, and indicated greater variability of the more heterozygous trees. These results, and others in the literature, suggest that the relationship of heterozygosity to homeostasis for fitness components is neither simple nor monotonic; it varies between scales of measurement, genetic backgrounds, and environments.