Horacio E. Bown

Vegetation diversity in the Santiago de Chile urban ecosystem

Summary This study took in urban and periurban areas of Santiago, Chile. The 967km2 metropolitan area is composed of approximately six million inhabitants from various social and economic backgrounds. The purpose of this paper was to assess alpha (α) and beta (ß) vegetation diversity in the 36 metropolitan boroughs, and analyze the relationship of the assessed biodiversity to social and economic indices. Preliminary results showed a tendency to increased vegetation diversity as the social and economic status of boroughs increased.

The influence of nitrogen and phosphorus supply and genotype on mesophyll conductance limitations to photosynthesis in Pinus radiata

Mesophyll conductance, g(m), may pose significant limitations to photosynthesis and may be differentially affected by nutrition and genotype in Pinus radiata D. Don. Simultaneous measurements of gas exchange and chlorophyll fluorescence were made to determine g(m), using the constant J method (Harley, P.C., F. Loreto, G. Di Marco and T.D. Sharkey. 1992. Theoretical considerations when estimating the mesophyll conductance to CO(2) flux by analysis of the response of photosynthesis to CO(2). Plant Physiol. 98:1429-1436), in a fast- and a slow-growing clone of P. radiata grown in a greenhouse with a factorial combination of nitrogen (N) and phosphorus (P) supply. Values of g(m) increased linearly with the rate of photosynthesis at saturating irradiance and ambient CO(2) concentration, A(sat) (g(m) = 0.020A(sat), r(2) = 0.25, P < 0.001) and with stomatal conductance to CO(2) transfer, g(s) (g(m) = 1.16g(s), r(2) = 0.14, P < 0.001). Values of g(m) were greater than those of stomatal conductance, g(s), and the ratio (g(m)/g(s)) was not influenced by single or combined N and P additions or clone with a mean (+/-SE) value of 1.22 +/- 0.06. Relative limitations to mesophyll conductance, L(m) (16%) to photosynthesis, were generally greater than those imposed by stomata, L(s) (13%). The mean (+/-SE) CO(2) concentration in the intercellular air spaces (C(i)) was 53 +/- 3 mumol mol(-1) lower than that in the atmosphere (C(a)). Mean (+/-SE) CO(2) concentration in the chloroplasts (C(c)) was 48 +/- 2 mumol mol(-1) lower than C(i). Values of L(s), L(m) and CO(2) diffusion gradients posed by g(s) (C(a) - C(i)) and g(m) (C(i) - C(c)) did not significantly differ with nutrient supply or clone. Mean values of V(cmax) and J(max) calculated on a C(c) basis were 15.4% and 3.1% greater than those calculated on a C(i) basis, which translated into different slopes of the J(max)/V(cmax) relationship (C(c) basis: J(max) = 2.11V(cmax), r(2) = 0.88, P < 0.001; C(i) basis: J(max) = 2.43V(cmax), r(2) = 0.86, P < 0.001). These results will be useful for correcting estimates of V(cmax) and J(max) used to characterize the biochemical properties of photosynthesis for P. radiata.

The influence of N and P supply and genotype on carbon flux and partitioning in potted Pinus radiata plants

Carbon (C) flux and partitioning responses of Pinus radiata (D. Don) clones to a factorial combination of nitrogen (N) and phosphorus (P) supply were estimated in small trees growing in a greenhouse over 44 weeks. Our objective was to use a C budget approach at the plant level to examine how a factorial combination of N and P additions and genotype modify gross primary production (GPP), net primary production (NPP), absolute C fluxes apportioned to aboveground net primary production (ANPP), aboveground plant respiration (APR), total belowground carbon flux (TBCF) and the partitioning of GPP to ANPP, APR and TBCF. Single N or P additions increased plant NPP and GPP similarly, but their combined effects exceeded those of their individual contributions. Nitrogen and to a lesser extent P additions enhanced carbon-use efficiency (CUE, NPP:GPP) and C partitioning to ANPP at the expense of TBCF. The fraction of GPP partitioned to APR was invariant to N or P additions. The ratio of soil respiration (FS) to TBCF was significantly greater in the low-N low-P addition treatment (61%) than in those treatments with single or combined N and P additions (49%). The slowest growing clone partitioned a significantly smaller fraction of GPP to ANPP (29%) than one of the faster-growing genotypes (33%). This research provides insight into how N and P regulate the C fluxes and partitioning in individual plants. Our results contribute to explaining clonal variation in aboveground growth rates and suggest that greater gains in CUE and partitioning to ANPP occur with addition of N rather than P supply.

Relating nutritional and physiological characteristics to growth of Pinus radiata clones planted on a range of sites in New Zealand

Six clones of radiata pine with known differences in growth rate were examined for clonal nutritional characteristics and for physiological determinants of clonal growth rate. We compared growth, foliar characteristics and nutrient, ¹³C and ¹⁵N concentration data for the six clones in 4- to 6-year-old field trials planted over a range of nutritionally contrasting sites. These data were also compared with growth, nutrient uptake and remobilization, foliar characteristic and gas exchange data from intensive physiological glasshouse experiments using 1- and 2-year-old plants of the same clones. Significant genotype x environment interactions in our field experiments conducted over strong nutritional gradients allowed us to identify radiata pine clones with consistent, superior growth and nutritional characteristics and clones that may be suited to particular site conditions. Our results suggest that the opportunity exists to exploit clone x site variation for site-specific clonal deployment and planting of fast-growing clones could be accompanied by planting of clones able to take relative advantage of site nutritional characteristics. Faster tree growth was not strongly related to any physiological characteristic, and the factors influencing growth rate differed among clones. The fastest-growing clone had consistent, high uptake of all nutrients, high fascicle weights and high water-use efficiency.

Chlorophyll fluorescence response of Pinus radiata clones to nitrogen and phosphorus supply

Chlorophyll fl uorescence responses to a factorial combination of nitrogen (N) and phosphorus (P) supply were measured in fi ve clones of Pinus radiata cultivated in a greenhouse over twenty-four months. Chlorophyll fl uorescence measurements were taken at months six (5 clones, 182 plants), nine (2 clones, 68 plants) and eighteen (2 clones, 48 plants). Plant growth in stem diameter, height, leaf area, fascicle mass, length and diameter were found to signifi cantly increase with N and, to a lesser extent, P additions; and these values were greatest when both N and P were combined. Plant growth and fascicle size also varied signifi cantly across clones and were generally consistent with the genotypic growth responses that were observed in the fi eld. Dark (Fv/Fm) and light-adapted (ΦPSII) photochemical effi ciency of PSII were found to signifi cantly increase with N and, to a lesser extent, P addition; and the combined effects of N and P exceeded those of the individual contributions. Stern-Volmer nonphotochemical quenching, which relates to the proportion of energy dissipated as heat, did not signifi cantly increase as plants became more N or P defi cient. Chlorophyll fl uorescence variables did not differ between clones. We found positive linear relationships between photosynthetic rates at 360 μmolmol-1 CO2 concentration and 1500 μmol photons m-2s-1 of irradiance (Asat), Fv/Fm and ΦPSII and both foliar nitrogen (Na) and phosphorus (Pa) concentration on a leaf area basis when a ratio of Na/Pa equal to 23 mol mol-1 was used to partition N from P defi ciencies. These relationships were independent of genotype. Chlorophyll fl uorescence and gas exchange estimates of electron transport were well correlated under ambient photorespiratory conditions, suggesting that chlorophyll fl uorescence variables are a good surrogate for gas exchange measurements in our experimental conditions. Se evaluaron las respuestas en fl uorescencia de la clorofi la frente a una combinacion factorial de adiciones de nitrogeno (N) y fosforo (P) en cinco clones de Pinus radiata cultivados en un invernadero por 24 meses. Se midio la fl uorescencia de la clorofi la en tres ocasiones: al sexto mes (5 clones, 182 plantas), al noveno mes (2 clones, 68 plantas) y al decimo octavo mes (2 clones, 48 plantas). El crecimiento en diametro, altura y area foliar de las plantas, y la masa, longitud y diametro de los fasciculos aumentaron signifi cativamente con adiciones de N y en menor medida con adiciones de P, y todas estas variables fueron maximas cuando ambos N y P se aplicaron en forma combinada. Las variables de crecimiento de las plantas y de tamano de los fasciculos tambien fueron signifi cativamente infl uidos por el genotipo los que ademas fueron generalmente consistentes con las respuestas observadas en los ensayos de campo. La efi ciencia fotoquimica del FSII de las muestras de follaje adaptadas a la oscuridad (Fv/Fm) y a la luz (ΦPSII) aumentaron signifi cativamente con adiciones de N y en menor medida con adiciones de P, y los efectos combinados de N y P excedieron aquellos de sus contribuciones individuales. El maximo quenching no fotoquimico (Stern-Volmer), el cual es un indicador de la proporcion de energia disipada como calor, no aumento signifi cativamente en la medida que las plantas fueron mas defi cientes en N o P. Las variables asociadas a la fl uorescencia de la clorofi la no difi rieron entre los clones. Se encontro relaciones lineales positivas entre las tasa de fotosintesis medida a 360 μmol mol-1 de concentracion de CO2 e irradiacion de 1500 μmol fotones m-2s-1 (Asat), Fv/Fm y ΦPSII, y las concentraciones foliares de nitrogeno (Na) y fosforo (Pa) expresadas sobre una base de area foliar cuando se utilizo una razon Na/Pa igual a 23 molmol-1 para separar defi ciencias de N de las defi ciencias de P. Estas relaciones fueron independientes del genotipo. Las estimaciones de transporte de electrones basadas en fl uorescencia de la clorofi la e intercambio gaseoso se encontraron bien correlacionadas bajo condiciones ambientales normales de fotorespiracion, sugiriendo que las variables asociadas a la fl uorescencia de la clorofi la fueron un buen estimador de las tasas de fotosintesis para nuestras condiciones experimentales.

Soil C/N influences the carbon flux and partitioning in control and fertilized mini-plots of Pinus radiata in New Zealand

H.E. Bown, M.S. Watt, P.W. Clinton, and E.G. Mason. 2011. Soil C/N influences carbon flux and partitioning in control and fertilized mini-plots of Pinus radiata in New Zealand. Cien. Inv. Agr. 38(2): 277-289. Patterns of carbon flux and partitioning were examined in highly stocked (40,000 stems ha -1 ) control and fertilized mini-plots of Pinus radiata D. Don at five sites, which covered a wide climatic and edaphic gradient on the South Island of New Zealand. The gross-primary productivity (GPP) and the partitioning of the GPP to the above- and below-ground productivity and respiration were determined using a carbon budget approach. All of the components of the GPP, the above-ground net primary productivity (ANPP [r 2 =

The influence of N and P supply and genotype on N remobilization in containerized Pinus radiata plants.

Una alta proporcion de todo el nitrogeno (N) utilizado en el crecimiento anual de la ampliamente distribuida especie forestal Pinus radiata proviene del N almacenado el ano anterior en los tejidos de los arboles. Sin embargo, no se sabe en que medida desbalances nutricionales, particularmente aquellos de fosforo (P), podrian cambiar la capacidad de esta especie de removilizar N. Consecuentemente, se evaluo la removilizacion de N en cuatro clones de P. radiata, sometidos a una combinacion factorial de N y P, en plantas creciendo en contenedores con arena en un invernadero por dos anos. Las adiciones de N fueron enriquecidas con 15N al 2.59%o (N marcado) durante el primer ano. Posteriormente las plantas fueron transferidas a arena limpia, creciendo durante el segundo ano con 15N a niveles cercanos a la abundancia natural de N (0.3664899 porcentaje atomico 15N, δ15N 0.5115%o). Los calculos de almacenamiento y removilizacion de N se basaron en la recuperacion de N marcado desde los nuevos tejidos durante el segundo ano de crecimiento. La removilizacion de N durante el segundo ano fue cinco veces superior en el tratamiento de alto-N alto-P (953 mg N planta-1), comparado con el de bajo-N bajo-P (199 mg N planta-1), e intermedio en los tratamientos con desbalance: alto-N bajo-P (422 mg N planta-1) y bajo-N alto-P (228 mg N planta-1). Al expresar la removilizacion de N como un porcentaje del contenido de N de las plantas al final del primer ano de crecimiento, se obtuvo que un 65% fue removilizado en el tratamiento de alto-N alto-P, comparado al 42-48% obtenido en los otros tratamientos al final del segundo ano de crecimiento. El cuociente entre la removilizacion de N y la absorcion de N por las raices fue mayor en los tratamientos con bajo N comparado con los de alto N, sugiriendo que los arboles removilizan proporcionalmente mas en la medida que la fertilidad declina. La mayor parte de la remobilizacion de N ocurrio en primavera-verano (77%), lo que coincidio con la mayor proporcion de desarrollo de las aciculas (80%), sugiriendo que la remobilizacion de N fue causada por la actividad de sus sumideros. El follaje antiguo fue la principal fuente de ciclaje interno de N, mientras que las raices el principal sumidero. Los clones de crecimiento mas rapido no mostraron una capacidad superior de remobilizacion, sugiriendo que el mayor desempeno en crecimiento inducido por el genotipo no es explicado por el ciclaje interno de N. En conclusion, las plantas sometidas a una oferta abundante y balanceada de nutrientes mostraron una mayor capacidad para removilizar N, comparado con aquellas plantas creciendo bajo limitantes unicas o conjuntas de N y P, y los clones que crecieron rapido no mostraron mayor capacidad para removilizar nitrogeno.

A potential nutritional modifier for predicting primary productivity of Pinus radiata in New Zealand using a simplified radiation-use efficiency model

The 3-PG (Physiological Principles in Predicting Growth) radiation-use efficiency model has been widely used and tested for predicting the primary productivity of forests all over the world. This radiation-use efficiency model accounts for plant nutrition through a user-defined dimensionless fertility parameter ( f N) that determines the effects a unit of radiation. Currently, this fertility parameter has to be entered by the user based on intuition or experience. The goal of this study was to propose a fertility modifier ( f N) for the radiation-use efficiency family of models based on soil chemical and physical variables. We determined gross- and net-primary productivity for a set of 10 intensively measured mini-plots of Pinus radiata D. Don on the South Island of New Zealand and then fitted a fertility modifier, f N, to the set of plots using a simplified radiationuse efficiency model. Fitted f N values were correlated to soil physical and chemical variables. The nutritional modifier, f N, significantly increased with the soil N (%) and decreased with the soil C:N ratio, and both, soil N and the C:N ratio, were measured in the upper 10 cm of soil ( f N = 1.32 – 0.04 C:N + 0.99 N, r2 = 0.73, P = 0.009). If confirmed, this relationship may prove useful to estimate the fertility modifier of radiation-use efficiency models ( e.g., 3-PG) for Pinus radiata plantations in New Zealand. However, caution should be exercised for sites where mineral nutrients other than nitrogen limit productivity. El modelo de eficiencia en el uso de la radiacion 3-PG (por sus siglas en ingles: Physiological Principles in Predicting Growth) ha sido ampliamente utilizado y probado para predecir productividad primaria de bosques en todo el mundo. Este modelo considera el estado nutricional de un cultivo a traves de un parametro de fertilidad ( f N) adimensional, definido por el usuario que reduce la efectividad de una unidad de radiacion en el modelo. De momento este parametro de fertilidad es ingresado por el usuario basado en intuicion o experiencia. El objetivo de este estudio consistio en proponer un modificador de fertilidad ( f N) para la familia de modelos de eficiencia en el uso de la radiacion basado en variables fisicas y quimicas de suelos. Para lograr este objetivo, se determino la productividad primaria bruta y neta en un conjunto de 10 mini-parcelas, medidas intensivamente, de Pinus radiata D. Don en la Isla Sur de Nueva Zelanda, posterior a lo cual se ajusto el modificador de fertilidad, f N, al conjunto de parcelas utilizando un modelo simplificado de eficiencia en el uso de la radiacion. Los valores ajustados de f N fueron correlacionados con una amplia gama de variables fisicas y quimicas de suelos. El modificador nutricional, f N, aumento significativamente con la concentracion de N en el suelo (%) y disminuyo con la relacion C:N del suelo, ambas variables medidas en los primeros 10 cm del suelo ( f N = 1,32 – 0,04 C:N + 0,99 N, r2 = 0,73, P=0.009). De ser confirmada, esta relacion podria demostrar ser util para estimar el modificador de fertilidad en los modelos de eficiencia en el uso de la radiacion ( e.g. 3-PG) para plantaciones de Pinus radiata en Nueva Zelanda. Sin embargo, se debe tener precaucion en el calculo de este parametro de fertilidad en sitios en los cuales nutrientes otros que nitrogeno limitan la productividad.