In the spring of 2017 I was contacted by Laboratorios Agrama to do with them what I thought was a very interesting essay on possible agronomic applications of xylem sap analysis (from now on SAX) in fruit crops.
The topic interested me because for almost 20 years this issue of SAX has been going around to try to give it a practical application in agronomy. But there are several pitfalls. The first is extraction, which is not easy. The methods used by the research centers were not easily transferable from day to day. And the methods that have been developed for a «simple» extraction, the truth is that they do not finish convincing, because normally they consist of pressing on a petiole until juices begin to come out at one end. These juices end up being a mixture of xylem sap, phloemics, parenchyma cells, …. And, secondly, another important problem is the analysis. First, get enough to analyze and then interpret what is being seen there. Again, the «simple» methods recently developed solve this issue in an expeditious way: the product obtained is added a reagent according to the ion to be determined and a portable colorimeter gives me the concentration of that ion, and the subject is considered to be resolved . Of course, these methods want a quick response of the nutritional status of the tree by analyzing the concentration of ions in their SAX. We will see that this is quite possibly their biggest mistake. Neither the method of extraction is the most appropriate, nor the method of analysis is not precise, nor the SAX serves to make a diagnosis of the nutritional status (and less immediate) of a woody.
What interested me the most about Agrama’s approach is the extraction method. It is a method based on a modified pressure chamber or Scholander chamber, used scientifically since 1965, which allows sap to be extracted from large terminal stems. As the volume of SAX extracted is large, and allows to obtain a vial of more than 5 ml, it can already be easily measured in a laboratory with spectrophotometric methods.
This is the chamber used:
And this is a summary of the method used for the extraction, in this case in citrus:
Another thing that interested me a lot of the approach proposed by Agrama is the utility of the model, of the whole method. We knew that the analysis of SAX does not serve to make a diagnosis of the nutritional status of a woody tree, but we do think that it could serve to make a diagnosis of the efficiency of the fertigation system. We thought we could find good correlations between the analysis of Fertilizer Solution, Saturated Paste Extract or Soil Solution (taken at the height of the center of the irrigation bulb, in the root system), the SAX and the corresponding leaf tissue analyzes. With these correlations we thought to make a model that would allow to correct and adapt the Fertilizer Solution applied in each period according to the actual rate of use by the plant.
And already with a previous trial of the method, carried out in a farm of orange trees and another one of almond trees in Palma del Rio (Córdoba), we started a campaign in 2018 in 3 farms and 4 crops (almond, orange, olive green and table grape). This is the approximate distribution of the parcels tested:
We set ourselves 4 samplings, which we did on May 10, June 29, August 1 and October 17 in some case and November 13 in some other. In each sample, we analyzed the ionic composition of: Fertilizer Solution (the mixture of Irrigation Water with the Fertilizer Salts corresponding to that period), Saturated Paste Extract (extracted with the Fertilizer Solution), SAX and foliar tissue.
Once the campaign is over, we begin to get involved with all the data obtained and we find ourselves with the following surprises:
When we calculate the ratio of ion concentration in SAX with respect to EPS we see that there are 3 macro ions that always appear much more concentrated in SAX than in EPS (PO43-, NH4+ y K+) and almost all the micros (B, Cu, Fe , Mn and Zn), less Mo, also appear much more concentrated in SAX than in EPS.
In general, the concentration of NO3– is very low and that of NH4+ is very high because normally the plant usually passes enzymatically all nitrates to ammonium for transport in xylem immediately after entering the root. Also noteworthy is the low concentration of Cl and Na, as well as Ca and Mg, in SAX.
On the other hand when we compare the relationships or ratios between related elements in the physiology of nutrition, such as the 4 groups: Ca/B – Ca/K – Ca/Mg, K/Cl – K/Mg – K/N, Na/Ca – Na/K – Na/Mg and P/Fe – P/Mn – P/Zn, in EPS and in SAX, we find this type of data:
We can simply see that the ratios between elements within each group are not the same outside the root as within the xylem, without responding to a common pattern, but the differences in some cases are very high and with some variation between samples.
We continue to entangle and we see that there is virtually no correlation between the concentration of Macroelement ions in SF and in EPS with respect to SAX. But there is a very good correlation between the SF and the EPS as expected!
However, the microelements do not behave the same, and we see that there is a certain correlation between SF and EPS and SAX, in some cases weaker and in others more consistent.
With the SAX values of macros and micros and the values of those elements in leaves we see that there are the same type of correlations, very bad with macros and somewhat better with micros.
The summary of all the correlations is shown below:
To try to unravel the skein we go back to review the literature on the subject, which is very extensive. Here I summarize some articles that have been very important for the conclusions:
- Xylem sap composition: a tool for investigating mineral uptake and cyclingin adult spruce. Etienne Dambrine, Francis Martin, Nathalie Carisey, André Granier, Jan-Erik Hallgren and Kevin Bishop. CRF-INRA. Plant and Soil 168-169:233-241. 1995.
- Xylem sap composition of beech (Fagus sylvatica L.) trees: seasonalchanges in the axial distribution of sulfur compounds. Heinz Rennenberg, Robert Schupp, Vjekoslav Glavac y Hubert Jochheim. Germany. TreePhysiology 14, 541-548. 1994.
- The chemical composition of xylem sap in Vitis vinifera L. Cv. Riesling duringvegetative growth on three different Franconian vineyard soils and as influenced by Nitrogen fertilizer. Andreas Peuke. American Journal of Enologyc and Viticulture 51: 329-339. January 2000.
- Xylem sap mineral analyses as a rapid method for estimation plant-availability of Fe, Zn and Mn in carbonate soils: a case study in cucumber. Nikolai Bityutskil, Kirill Yakkoonene, Anastasiya Petrova y Marina Nadporozhskaya. Universidad de San Petersburgo (Rusia). Journal of SoilScience and plant nutrition. Vol. 17 nº 2. Temuco. Junnuary 2017.
- Xylem sap sampling-new approaches to an old topic. Ulrich Schurr. Universidad de Heidelberg (Alemania). Trends in Plant Science. Vol. 3 nº 8. August 1998.
- Seasonal dynamics of nutrients in leaves and xylem sap of coffee plants as related to different soil compartments. Maya Bundt, Sigrid Kretzschmar, Wolfgang Zech y Wolfgang Wilcke. Universidad de Bayreuth (Alemania). Plant and Soil 197: 157-166. 1997.
- Seasonal variations in mineral concentrations in the trunk xylem sap of beech (Fagus sylvatica L.) in a 42-year-old beech forest stand. V. Glavac, H. Koenies y U. Ebben. Universidad de Kassel (Alemania). New Phytology 116, 47-54. 1990.
- The xylem sap of maple (Acer platanoides) trees-sap obtained by a novel method shows changes with season and height. Volker Schill, WolframHartung, Birgit Orthen y Manfred Weisenseel. Universidad de Karlsruhe(Alemania). Journal of Experimental Botany. Vol. 47, nº 294, pp. 123-133. January 1996.
Almost all the works are German (with some French, some American and some Russian), and almost all of them are also dated from the middle to the end of the 90s. But they end up giving us the key. The bibliography finishes confirming the data that we have been able to see in our essay and that can be summarized in the following points:
- Unfortunately, we can confirm that wood-based xylem sap data can NOT be used to diagnose the efficiency of the fertigation system. But we have learned a lot from a woody’s nutrition.
- A fruit tree needs to have a soil solution rich in nutritious ions for its development. The tree is taking, in a process of normal absorption, all this water with ions in solution, passively and actively, and most of it accumulates in reserves, with greater or lesser intensity, in roots, trunk and main branches.
- The composition of the SAX in each of the parts of the tree is not the same. We have been taking the final sprout SAX which is the tree’s richest sap.
- The tree is carrying the xylem in a small part directly from what it takes root, and mostly by mobilizing the various reserve organs that it has throughout its architecture, even feeds the final xylem from the phloem.
- Therefore, the SAX of an outbreak of a fruit tree can not be used to correlate with the Saturated Pasta Extract or Soil Solution in root, or with the Fertilizer Solution applied, neither instantaneously nor in the medium term, because the tree changes the composition of the SAX according to the seasons, the phenological stage, the sprouting, the growths, the fructification, the biotic or abiotic stress, …, which invalidates the method for an agronomic utility on the fertilization system.
- In fact, as discussed in one of the articles cited, how can we think that a woody crop will make its growth, development or fruition needs depend on the precise composition of the soil solution? And it is true! It is not logical to think that. Especially when the strategy of a woody is based on the immense possibility of accumulating reserves, with respect to any herbaceous plant!
- One could work on the correlations that have been found between the concentration of ions of microelements in the solution of soil in the root zone and within the xylem sap, in case it would be useful.
Despite this negative conclusion on the initial thesis, we are not discouraged and we are going to teste this 2019 on different herbaceous horticultural crops, to see if we can use the method!